What was going on when I was born?

LUCY The Beginnings of Humankind. By Donald C. Johanson and Maitland A. Edey. Illustrated. 409 pp. New York: Simon & Schuster. $16.95. THE story of human evolution - how apelike animals living millions of years ago changed into the human beings of today - is one of the great scientific epics of all time. But, like the sagas of the ancients, the details of the hominid odyssey have tended to vary with the teller. During the past 20 years, and especially during the past 10, significant rewritings have appeared; unfortunately for anyone seeking a clear interpretation of human evolution, most have been based as much on changing opinion and ideology as on new evidence. ''Lucy: The Beginnings of Humankind'' is, therefore, a welcome and needed corrective. Dr. Donald Johanson is a paleoanthropologist, based at the Cleveland Museum of Natural History, whose fossil discoveries since 1973 have forced a major reinterpretation of the early stages of human evolution. Maitland Edey is a first-rate science writer and the author of the excellent and popular volume ''Early Man.'' Together, in clear engaging prose, they trace the rocky history of efforts over the past century to find and interpret the most significant hominid fossils, while at the same time they tell of Dr. Johanson's own remarkable fossil discoveries in Ethiopia.

''The missing and murdered children'' is spoken as a single word here in a distraught city frustrated by the baffling, unsolved deaths of 18 children and the mysterious disappearances of two others in the past 19 months. Two new names, one of a dead child and one of a missing boy, swelled the list to 20 black victims yesterday while city officials were saying that they were conducting the most extensive investigation in the nation's history. Yet they say they are no closer to arresting suspects than they were when an investigative task force began work last summer. So far, the investigators have tried everything from filming funeral services to consulting with psychics. Citizens have formed mass search parties to look for victims and have established groups to seek children under the age of 17 who are violating the 7 P.M. citywide curfew. City firefighters have walked door-to-door asking for scraps of information and distributing pamphlets on child safety. Agents of the Federal Bureau of Investigation have come from around the country, forming teams each day to scour woods and deserted areas for victims.

Mark Aguirre scored 24 points tonight but he might have easily made it 30 or more as he led De Paul to its 10th straight victory and 23d of the season by beating Marquette, 78-71, at the Horizon. ''We had to tell him to shoot,'' said Ray Meyer, the Blue Demons' coach. ''Sometimes it's frustrating when Mark starts passing off so much. He gave up a couple of easy 15-foot shots out there. But then, we won, didn't we? And a wise old man once told me, 'You can't do any better than win.' ''

The Economics of Hope Some private economists are skeptical of the Reagan Administration's inflation projections, which seem to be more of a hope than a forecast. According to the President's economists, tax cuts, reductions in government spending and tight monetary policy will bring inflation down from 11 percent this year to just over 8 percent in 1982, and to 6.2 percent the year after. By 1986, Mr. Reagan forecasts that the Consumer Price Index will show an annual increase of 4.2 percent. Economists like Lawrence Chimerine of Chase Econometrics and Michael Evans of Evans Economics feel the President is overly optimistic. While both men expect inflation to drop over the next five years, they doubt that productivity, which they feel is the key to lower inflation, will improve as rapidly as the President expects. Moreover, they point out that wage increases, which have been running behind the rate of inflation, may average 12 percent for the next few years, further damaging the outlook. Finally, the Reagan forecast seems to assume stability in the world petroleum market, a luxury that disappeared in the early 1970's.

WHITE PLAINS ALTHOUGH the murder trial of Jean S. Harris has been the longest in recent memory in Westchester County, law enforcement officials say, it has not had an adverse impact on the judicial system here, which was already overburdened when pretrial hearings in the case began last Oct. 6. For more than four months, the trial consumed the efforts of Judge Russell R. Leggett and his staff, plus a Clerk and Court Reporter. ''This has been one of the longest trials in the county's history,'' said a spokesman for Justice Joseph F. Gagliardi, Administrative Judge for the Ninth Judicial District. ''But, it has not delayed other cases. We have not been affected adversely by the Harris trial.''

''The Dogs of War'' is not a watershed movie, the sort that somehow changes the look of - and response to - all movies that come after. Yet it represents the kind of movie that, in this era of increasingly predictable entertainments, resolutely refuses to take the easy way. It invites speculation. You might call it a long-shot film. A long-shot film is not necessarily a movie composed primarily of long shots, of panoramic vistas and such. Rather it's a film that keeps its characters at a comparatively chilly distance and, in this way, encourages the audience's active interest in what's going on and why. It allows us to make our own conclusions. As medium shots and long shots in a film invite the audience to look where it will, a movie like ''The Dogs of War'' invites us to make decisions about Shannon, its mercenary soldier hero, and what he's up to. The longshot movie doesn't insist on telling us what to think.

Don Maloney, reunited with his regular linemates in the second period, scored three goals within 2 minutes 30 seconds to rally the New York Rangers to a 6-4 victory over the Washington Capitals last night at Madison Square Garden. Maloney, playing with Eddie Johnstone and Mike Allison, scored his 22d goal at 16 minutes 41 seconds to put the Rangers in front, 3-2. He beat Mike Palmateer, the Washington goaltender, on a rebound of Ron Greschner's shot from the right point. Washington's Dennis Ververgaert was in the penalty box.

Government and private agencies are taking steps to rebuild the supply of hotel housing for the elderly poor in Manhattan, many of whom have been displaced from single-room occupancy hotels as the buildings convert to market-rate housing. According to Anthony B. Gliedman, the City's Housing and Preservation Commissioner, the agency is channeling immediate lowinterest Federal loans to two facilities, the Woodstock Hotel at 127 West 43d Street and the Hudson Hotel at 1649 Amsterdam Avenue. Both will receive 3 percent loans for basic improvements to provide housing for the poor. The Woodstock, which was taken over by the city five years ago for nonpayment of taxes, will receive $266,000. The Hudson has been allocated $450,000. This hotel was also taken over by the city nearly five years ago after Albert Blue, who is now its administrator, could not longer maintain operation of the 132-room hotel. ''Taxes in arrears totaled $75,000 and we were never able to pay it off because so much money was eaten up for repairs,'' Mr. Blue said, citing the complaint most frequently heard regarding S.R.O.'s.

WHITE PLAINS WESTCHESTER should be allowed to continue dumping sewage sludge in the ocean and, if necessary, should carry it out to the edge of the Continental Shelf, rather than follow a consultant's advice and spread it on open land in the county, County Executive Alfred B. DelBello said last week. Mr. DelBello sent a position paper to the Congressional delegations from New York and New Jersey opposing the consultant's report, which cost $249,000 and took two and a half years to complete. The consultant's report suggested 11 open areas as possible sites. Officials of the municipalities in which the sites are located unanimously opposed dumping. Five of the sites are in Cortlandt, two each in Ossining and New Rochelle, and one each in Croton and Greenburgh.

The Reagan Administration's budget offers the states greater flexibility in handling Federal aid, but at the cost of revenue cuts that will cause ''dislocation for state budgets,'' the nation's governors were told today. An analysis of President Reagan's proposals, prepared by the National Governors Association and the National Conference of State Legislatures, noted that except for cuts in Medicaid, sewage treatment and mass transit funds, the budget reductions generally avoided areas where state governments would have to pick up the cost. The study also warned the states to expect sizable reductions in corporate tax revenues and predicted that ''a large proportion'' of the additional $6.3 billion in budget cuts to be specified March 10 would affect state aid. Mr. Reagan's $695.5 billion budget for the next fiscal year, which begins in October, would be higher than the estimated budget of $654.7 billion for the current fiscal year. The Administration said it would be $41.4 billion lower, however, than what current programs would cost if no changes were made.

''Hath not a Jew eyes? Hath not a Jew hands, organs, dimensions, senses, affections, passions? - fed with the same food, hurt with the same weapons, subject to the same diseases, healed by the same means, warmed and cooled by the same winter and summer as a Christian is? If you prick us, do we not bleed? If you tickle us, do we not laugh? If you poison us, do we not die? And if you wrong us, shall we not revenge?'' Like almost everything Shakespeare wrote, Shylock's famous speech in ''The Merchant of Venice,'' can be read in many ways. Is Shakespeare making a plea for the common humanity of all men? Or is he putting a sophistical speech rationalizing revenge in the mouth of a villain? In Shylock, did he create a portrait of an honorable man victimized by hypocritical Christian society? Or did he set up a pernicious stereotype of the Jew as a greedy, vengeful moneylender? Because of the nature of these questions, the ambiguities of ''The Merchant'' are not simply matters of literary criticism, but highly emotional matters with the gravest social, historical and religious consequences.

The Reagan Administration has decided to ask Congress for about $2.5 billion next year to begin building a fleet of new long-range bombers capable of penetrating Soviet defenses well into the next century, according to Pentagon officials. The decision, fulfilling a pledge made by President Reagan in the election campaign, has come as Secretary of Defense Caspar W. Weinberger and his staff have been striving to complete their revised 1982 military budget, which is scheduled to be submitted to Congress on March 10. Administration officials said that no decision on which bomber to build had been made and that it most likely would not be made until June, after the completion of a study of the options, ordered by Mr. Weinberger. Internal Disputes Criticized With that question still open, Gen. Alton D. Slay, who retired this month as head of the Air Force command that develops new aircraft, admonished his four-star colleagues to stop arguing among themselves and agree on which bomber they want.