What was going on when I was born?

The Secretary General of the United Nations, Javier Perez de Cuellar, announced today that, in a change of plans, he would visit Iran and Iraq during his Persian Gulf tour to try to help end the war between the two countries. Mr. Perez de Cuellar, who made the announcement in Doha, Qatar, will fly to Teheran on Sunday and to Baghdad later in the week. In a visit here five days ago, he said he would not visit the two warring countries during his tour because Iran had refused to give assurances that it was willing to discuss a comprehensive settlement of the four-and-a-half-year- old war. 'A Positive Development' The Secretary General now feels that his conditions have been met, according to an aide reached by telephone in Doha.

. . . THE HEAVENS AND THE EARTH; A Political History of the Space Age. By Walter A. McDougall. Illustrated. 555 pp. New York: Basic Books. $25.95. A GRADE-SCHOOL youngster once wrote to T. Keith Glennan, the administrator of NASA, saying she wanted to know ''everything about space.'' In the margin of her letter Mr. Glennan scribbled ''So do I.'' So too does Walter McDougall, a historian at the University of California, Berkeley. ''. . . The Heavens and the Earth'' is just as cosmic and all-encompassing as its title suggests.

THERE is no other firm in the world quite like Merrill Lynch & Company. It is the giant of the brokerage industry, from New York to London to Tokyo. In the United States, Merrill's brokerage offices have been known for decades in nearly every hamlet in the land - about 90 percent of all Americans live within 20 miles of a Merrill branch. More recently, the firm has elbowed its way into the upper echelons of investment banking, becoming a major force in the world of high-stakes corporate finance. But the giant is faltering. Its 1984 financial results were dismal. Merrill earned $95 million, compared with $230 million the year before - on revenues in the same $6 billion range. Its pre-tax profit margin was a slim 1.2 percent, and its 4.8 percent return on equity was far below the industry norm.

To say that a dream came true with the back-to-back Broadway openings of Peter Nichols's ''Joe Egg'' and Neil Simon's ''Biloxi Blues'' is not to indulge in idle rhetoric. The dream that came true was an actual dream - the one in which the dreamer runs into some old friends and discovers, to his amazement, that the familiar faces and personalities have suddenly been altered almost beyond recognition. So it is in the two productions that have lifted a moribund Broadway season from its ides of March (''The Octette Bridge Club,'' ''The Loves of Anatol,'' ''Requiem for a Heavyweight'') to an Easter-eve near- resurrection. In ''Joe Egg,'' two comic actors of New York theatergoers' long acquaintance, Jim Dale and Stockard Channing, have turned themselves inside out to provide performances that are as shattering as they are funny. In ''Biloxi Blues,'' an even older friend, Mr. Simon, has written his most heartfelt comedy - with the result that we can never again pigeonhole a writer who had become the most popular American playwright in part by becoming the most cautious.

-Nimeiry lost power in the Sudan yesterday the way he won it 16 years ago - by a military coup. It was in large measure the price for yielding to the United States and the International Monetary Fund, which had pressed him to impose austerity on a people already burdened by poverty. In Washington last week, he reaped a reward - $67 million in economic assistance that the Reagan Administration had been withholding and another 225,000 tons of grain for some 6 million starving people.

IT is an axiom, maybe even a cliche, but Manager Dave Johnson cannot help voicing it when he peers into the new season and evaluates the Mets' chances of finally making it to first place: ''We're going to go as far as our pitching takes us.'' If so, the Mets may be facing a more arduous time than they foresaw six weeks ago, when they opened spring training in a mood of buoyancy and great expectations. And they had good reason for joy: They surged from last place to second in the National League's East in 1984, then acquired Gary Carter from the Montreal Expos in December and prepared to confront the world with new power to go with all that young pitching. But, in the last two weeks, the young pitching has begun to come apart, and Johnson has been forced to realign his staff just before the curtain is raised on the new season.

RICKEY HENDERSON thinks he plays better against teams in the American League's Eastern Division than he does against the Western Division teams. ''The teams in the East are really competitive,'' says Henderson, who this year has moved from the West (Oakland) to the East (Yankees). ''They have all those great players. I feel I'm in that class and my performance is better.'' Don Baylor knows what his teammate means. ''I think there's a different caliber of play in the East,'' says Baylor, who has played for two teams in each division. ''It's better in a lot of ways. I've played in both divisions and I've enjoyed playing in the East more. When you go to the West, it's a little different. When I was in California, I missed the competition there is in the East. My batting average is better against the East than the West.'' Six of the Eastern teams will start this year's competition tomorrow as the baseball season opens with a schedule of five games, four in the American League. And there is, as Henderson and Baylor believe, much to show that the American League East is baseball's best division.

GABRIEL GARCIA MARQUEZ is in the midst of a new novel, and a predictable order is imposed on his life. The 1982 Nobel Prize in Literature is behind him and so is the publication of his most recent novel, ''Chronicle of a Death Foretold.'' Still, his fans seek out the 57- year-old author of ''One Hundred Years of Solitude'' - the book that made him a celebrity. His days now are like his writing - planned meticulously and carried out with carefree style. After six hours at the typewriter, he divides the remainder of the day between reading and listening to music, and friends, writers, politicians - people he calls my ''critics, protectors and co-conspirators.'' At times he lives in Cartagena, on Colombia's Caribbean coast, not far from where he was born. The area remains a rich source for him, replenishing his imagination with the myth and anecdote that find their way into his writing. But he and his wife, Mercedes, always return to the highlands and Mexico City, where he writes in the privacy of a studio in his garden. This is where the shy yet gregarious writer and I talked in late February. He has said that his novel in progress has to do with aging. I asked him to discuss his approach to old people in fiction: You're writing a happy love story, as you've called it, a love affair between two very old people.

ALTHOUGH the sponsor of a cooperative conversion is required by law to set up a reserve fund, there has been little agreement over the years on the most prudent way to manage and replenish the fund, how much should be kept in it - or, indeed, whether a fund is really necessary. Some co-op boards prefer to use up the original amount and then take out a loan or call for a special assessment whenever they need large sums for emergency repairs or major improvements. Others are uneasy about large-scale borrowing because they say they can never be sure how much they will incur in interest charges, or whether a loan will be readily available at the moment of need. Directors in more modest neigborhoods worry about their tenant-shareholders' ability to meet a special assessment or to pay extra maintenance to keep restoring the fund. So they are constantly seeking ways to replenish it.

The 15-year-old Government of the Sudan was overthrown today in a military coup led by the Defense Minister, according to statements by the new Government. The takeover came after more than a week of demonstrations and strikes touched off by increased food prices and growing disaffection with President Gaafar al-Nimeiry's Government. It occurred while Mr. Nimeiry, a 55- year-old army officer regarded as pro- Western, was out of the country. He arrived in Egypt today after more than a week in the United States.

IF SPRING TRAINING was any indication, this could be the year that George Steinbrenner changes not managers, pitching coaches and hitting coaches but doctors, trainers, strength coaches and masseurs. Pitching was supposed to be the Yankees' primary question entering the season, but maybe the players' health looms even larger in the team's chances. The season hasn't even started - it does tomorrow, in Boston - and the Yankees already have four players on the disabled list. If they overcome the spring siege of injuries and - surprise - win the division title, maybe the doctors and trainers should be named the most valuable performers.

Major League Previews New and exciting as they may be, the Mets are not quite ready to win the National League East, says Joseph Durso. His pick is the Cubs, who won the division last year only to lose to the San Diego Padres in the playoff. If the Cubs win the division, they would most likely find a familiar opponent, the Padres. Murray Chass likes the Toronto Blue Jays in the American League East and the Yankees to finish fifth. In the West, the Minnesota Twins, once a power in the division, may have enough to return to prominence.