What was going on when I was born?

Call Whoopi Goldberg a comedienne and she shakes her head so vehemently that her pixie-like face almost disappears under an umbrella of tiny corkscrew braids. Call her an actress and she laughs because, she says, the image that comes to mind is ''like tweaking a cheek,'' and she is not a person who would stand for cheek- tweaking. No, she says emphatically, she is not an actress. Well, Whoopi, what are you? ''I'm an actor,'' she says, without hesitation.

The Reagan Administration decided today to reduce significantly the size of the United States Embassy staff in Beirut as a result of continuing security threats, State Department officials said. One official said the move would reduce the number of official American personnel to about 30, from 45 on Friday. The embassy staff on Sept. 20, when the substitute embassy building near East Beirut was bombed and two Americans were killed, included 99 Americans. Total Was 190 in 1983 Officials also noted that on April 18, 1983, when the original American Embassy building in West Beirut was destroyed by a car bomb, there were 190 United States personnel there. But at that time the United States was actively involved in all facets of Lebanese life, supplying the Lebanese Army with military equipment and advisers, undertaking a large-scale aid program and trying to bring stability to Lebanon's political life.

When the historic breakup of the American Telephone and Telegraph Company was announced in January 1982, executives at scores of telecommunications companies were certain that a huge, lucrative market had been laid at their feet. ''It's what we've been pushing for for a long time,'' William G. McGowan, chairman of the MCI Communications Corporation, said the day he heard the news. Mr. McGowan probably winces when he remembers those words now. On Monday, MCI reported a plunge in quarterly profits from 1983. In addition, its third- quarter revenues actually dropped from the prior three months. Its main source of comfort is that none of its competitors - including A.T.& T. itself - is doing any better. The year 1 A.D. (after divestiture) has proved a bonanza of sorts for consumers, who have seen prices for long-distance phone service and telephone equipment plummet as myriad companies battle for their business. But it has been a brutal year for MCI, ITT, GTE-Sprint, and other contenders for shares of what had once been the domain of A.T.& T. For them the Jan. 1 breakup of the old phone monolith has brought price wars, management shake-ups, foreign competition, depressed profits - even red ink in some cases - and plunging stock prices.

Government officials said today that senior American military officers had begun to move more freely around El Salvador. But they denied there had been any changes in rules barring advisers from combat. Questions about their role arose Friday after three advisers assigned to the United States Embassy were seen near Perquin, near the site of a battle between Government soldiers and rebel troops. American diplomats in San Salvador said the rules governing adviser activities appeared to have become more flexible.

LAST summer, Democratic strategists targeted foreign affairs as President Reagan's most vulnerable area and laid plans for a campaign building to a foreign- policy crescendo in late October. Even in September, when Walter F. Mondale was floundering, his aides resisted turning from deficits and taxes to foreign policy. ''The time for that is October,'' one of them firmly insisted. Deliberately, the Mondale camp fought for and won agreement for what has become a make-or-break event, the second Presidential debate, on foreign policy, in Kansas City tonight. In that sense, the political script has followed the Mondale scenario, though 16 days before the election the former Vice President lags farther behind than his lieutenants wanted. But the Democratic nominee has pulled up from still farther back. Yesterday's New York Times/CBS News Poll put President Reagan 13 points ahead. The week before the first Presidential debate, on domestic policy issues, he led by 23 points.

LONDON Most of the 40,000 to 50,000 United States businessmen and businesswomen living here will go home three, four or five years from now - back to the land of efficient telephones, relatively docile trade unions and cold beer. But there are other Americans who settle into London more or less permanently. Some stay because they like the city's ambiance, its civility, its sophistication, its rich social and cultural life. Some remain because they find exceptional opportunities here. And some stay in England simply by chance. They tend to lead thoroughly British lives; their employees and most of their friends are British. And they look down a little, although they wouldn't admit it, on their compatriots who spend the bulk of their time in Britain surrounded by Americans at work and play. The American colony in London is probably the largest in Europe, and some of its members play highly prominent roles in British life, enjoying a fame that American expatriates don't often attain elsewhere abroad. The common language certainly has something to do with their ascendency,, and the pro-business climate engendered by the Tory Government has not hurt.

Television is not just showing us the Presidential and Vice Presidential debates; television is determining how we score them, too. What plays well is what wins. The Founding Fathers may have reckoned that truth would drive out error after careful deliberation, but that was before the cathode ray tube and coaxial cable. Old-style political discourse, imperfect as it was, rested on the assumption that candidates were divided by issues, and by issues they would be judged. New-style television discourse operates under different rules. Do the candidates have presence? Are they showing lots of zip? When we hunker down in our living rooms tonight to watch Ronald Reagan and Walter F. Mondale discuss war and peace, the new rules invite us to be theater critics. It is not the issues we are asked to judge; it is the nuances of the presentation.

Conventional shopping-center-development wisdom says that malls need ''anchors'' - the large department, food or home-improvement stores that pull in shoppers. But last week, ground was broken for Philips Plaza, a shopping center in Lynbrook, L.I., to be composed of nothing but clothing boutiques and small specialty stores.

SONIA is 16 years old and she has learned that she is going to have a baby. She is not married, and she is frightened. Marianne was 18 when she learned she was going to have a baby. She was not married. She was frightened. Marianne is a Yonkers resident. Sonia is a cartoon character, part of a new intiative to address the increase in teen-age pregnancies in the county. Marianne is part of that growth, one of the 2,374 county women between the ages of 10 and 19 who became pregnant last year, 19 percent more than a decade ago. Earlier this month, the county's Department of Social Services unveiled Sparks - Some Plans of Action that Relate to Kids - at the Yonkers Public Library before an invited audience of educators and social agency representatives.

The men of El Salvador interrupted four years of killing last week, but only for a moment. Unarmed leaders from both sides got together and took a hesitant first step toward peace. Then they went back to warmaking.

ON A recent afternoon, Sgt. Bernard M. Poggioli, head of the Youth Services Unit of the Port Authority of New York and New Jersey, stood on the roof of the bus terminal on Manhattan's Eighth Avenue, scanning the crowds below for faces from missing-persons posters. ''We want to return missing kids to their homes or, if abused, to shelters or foster homes,'' the authority police officer said. ''Above all,'' he added, pointing to the street, ''to prevent them from falling into the hands of the criminals down there.'' Last year, 2,800 youths, 375 of them from New Jersey, were reported missing to Sergeant Poggioli's unit or were helped in the terminal by its three plainclothes officers. (Besides the officers, the unit includes three social workers and a statistical clerk).

Perhaps nothing in modern science inspires quite as much guesswork as who will win the Nobel Prizes. Nominators are a tight- lipped bunch, and the process by which the Swedish Academy of Science and Stockholm's Karolinska Institute cull through candidates' credentials is a carefully guarded secret. Still, many expected this year's award for medicine to go to three immunologists - Dr. Cesar Milstein of England, Dr. Georges J.F. K"ohler of Switzerland and Dr. Niels K. Jerne, who was born in Britain and raised in Denmark - for their work developing monoclonal antibodies, biological bullets that may one day be used to ''seek and destroy'' cancer cells. Last week, it did.