What was going on when I was born?

The assertion last week by Treasury Secretary James A. Baker 3d that ''the median-income family'' in every state would be better off under the Reagan Administration's tax plan is not borne out by an analysis of Government statistics. The figures show that in New York and several other states, couples with two wage-earners, two children, typical deductions and the median income for a family of that size in their state would owe slightly higher taxes under the Reagan proposals than they would owe if the law is not changed. Mr. Baker's assertion, in testimony before the Senate Finance Committee, was based on the premise that a family with median income - the level at which half the families earn more and half earn less - had only one wage-earner. Study of 2-Paycheck Homes Internal Revenue Service statistics show, however, that two-thirds of the couples earning between $30,000 and $40,000, the range where the median income falls in most states, have two wage-earners. Those families, under the present law, are entitled to a tax deduction that the President proposes to abolish.

President Reagan in a speech in New Jersey last week reasserted his belief that his tax plan would not hurt taxpayers in ''high-tax'' states such as New York. But neither the President nor his lieutenants have ever denied that many New Yorkers would face a big tax increase. And while Governor Cuomo has insistently denounced as unfair a key Reagan provision, the proposal to end the deduction for state and local taxes, the Governor has not contested that a great many New Yorkers - not all of them rich - would enjoy substantial tax cuts. The dispute heated up this weekend, when Patrick J. Buchanan, the White House director of communications, described Mr. Cuomo as a ''glib, fast-talking lobbyist for a reactionary liberalism that would kill tax reform in its crib.'' The charge was made in a letter to The New York Times.

President Reagan today warned Moslem Shiite hijackers ''for their own safety'' to free the American hostages on a Trans World Airlines jet in Beirut as well as the passengers removed Friday night to an undisclosed location. Mr. Reagan, who met this afternoon with advisers, also affirmed the United States policy of refusing to negotiate with terrorists. ''This has always been a position of ours,'' said Mr. Reagan, who returned early from a weekend at Camp David, Md., to confer with aides. At Least 40 Hostages The hijackers have killed one passenger and are holding at least 40 Americans hostage in Lebanon.

A political bargain that limits deployment of the MX missile, as well as problems with the planned Midgetman missile, have cast new doubt on the future of land-based missiles in the country's nuclear arsenal, according to Pentagon officials and members of Congress. The officials and some lawmakers say they are worried that the United States in the next decade will become dangerously dependent on missile-carrying submarines and bombers to retaliate in the event of a nuclear attack. The Reagan White House, like the previous Administration, has expressed steady concern that existing land-based missiles are vulnerable to a Soviet surprise attack and that the missiles are aging while the Soviet Union is improving its force. Problems Facing Midgetman The MX, a huge 10-warhead intercontinental missile favored by the Administration, has encountered relentless political opposition, and most Administration officials have abandoned hope that it will become the mainstay of the missile force. In addition, many strategic planners said, little notice has been given to formidable problems facing the Midgetman, a smaller, single-warhead mobile missile that is favored by many Democrats as a long-term solution.

Andy North had not won a tournament since taking the 1978 United States Open and did not seem destined to win today in the final round of the 85th Open - not unless something happened to Tze-Chung Chen, who led by four shots with 14 holes to go at Oakland Hills Country Club. Then, in one of those inexplicable twists, Chen took a quadruple bogey 8 at the par-4 fifth hole to open the door for North and three others still in the running. Chen struck his ball twice on one stroke, suffering a one-shot penalty as he got that 8. North was the only one able to take full advantage. Despite one of the poorest final rounds by an Open champion in the last half century, North's four-over-par 74 was just good enough for to finish at one-under-par 279 and beat Chen, Denis Watson of South Africa and Dave Barr of Canada by one shot.

When the Chicago commodity exchanges introduced financial futures a dozen years ago, they revolutionized the global money market by affording investors and dealers in Government and private debt issues the ability to hedge their portfolios and trading risks. Next Friday, New York's Coffee, Sugar and Cocoa Exchange will start trading involving an even more radical concept in futures - contracts based on the Government's wage and salary component of the Consumer Price Index (C.P.I.-W). Basically, the C.P.I.-W futures permit the hedging of pensions, annuities, insurance policies and indeed any contract or business transaction that could be adversely affected by inflation. ''Until now, inflation hedgers and speculators could only do so indirectly through the use of financial futures and options that respond to changes in interest rates,'' said Todd E. Petzel, chief economist of the 103-year-old Coffee, Sugar and Cocoa Exchange. ''But this indirect method often did not provide sufficient inflation insurance.''

The Argentine economy and its intractable inflation problem has toppled governments and ruined the political careers of a slew of bright financial ministers for more than four decades. Now, President Raul Alfonsin, a man who came to power promising his countrymen a better life, has proposed the most radical program in the nation's history. It will mean a dramatic short-term drop in the Argentine standard of living and will require a long, difficult road to recovery, economists said. Mr. Alfonsin has frozen wages and prices and has issued a new currency that he says will not lose its value, fixed at $1.25.

Mikhail S. Gorbachev may have had little or nothing to do with the recent release of the film ''Agoniya.'' Yet it was symptomatic that people were quick to credit the new leader with being responsible for bringing out the film, which is about the last days of the Romanov dynasty. It had lain on the censor's shelf for more than a decade - because, in the view of many here, the Soviet authorities were not willing to have Czar Nicholas II portrayed as a bewildered human being overwhelmed by history. In the past, Muscovites would have said that the film had been released despite the leader. Now they seemed anxious to treat the event as added evidence that a new day had dawned in the Kremlin.

The city's Transportation Department is proposing to make 42d Street a one-way, westbound thoroughfare for automobiles, with bus lanes in both directions, to expedite traffic for the Jacob K. Javits Convention Center on the West Side. The proposal, which has not yet been submitted to Mayor Koch or the Board of Estimate, would re-route eastbound traffic to 43d Street, which now carries westbound traffic, and to 40th Street. In a first, experimental phase, the plan would alter traffic on the six lanes of 42d Street with road markings, signs and enforcement. If the experiment were a success, sidewalks would be narrowed and concrete islands for loading and unloading bus passengers would be built.

CHICAGO A BATTLE rages in Chicago over the baseball team on the North Side, officially the Chicago National League Ball Club Inc., but better known as the Cubs, or - to the incurably passionate - the Cubbies. Specifically, the battle concerns the Cubs' ball park: To put lights or not to put lights in Wrigley Field, that is the question. The battle has been raging for more than three years now, and it is getting hotter. It is conceivable that if the Cubs, the defending National League East champions and currently in second place, are involved in postseason play they will play their games not in Wrigley Field, nor even in Comiskey Park, home of the White Sox of the American League. Dallas Green, the Cubs' president and general manager, has suggested that the games could be played in some distant National League hippodrome, such as Riverfront Stadium in Cincinnati or Busch Stadium in St. Louis.

Police and army units in armored vehicles used tear gas and rubber bullets in this vast and bleak township outside Johannesburg today to disperse thousands of black people commemorating the ninth anniversary of an uprising. Despite calls by some clerics for prayers for the overthrow of the white minority Government to mark the day, however, the mood seemed almost an anticlimax compared with the passion voiced in advance. For South Africa's black majority, June 16 is one of the most highly charged days of the year. The day in 1976 was the start of an uprising that spread from here and claimed more than 500 lives before the unrest eased in 1977. #4,000 at Ceremony Today, about 4,000 black people crammed into Regina Mundi Cathedral in Soweto to hear a blend of hymns and political proselytization while police and army units waited outside. Churches are one of the few places where blacks may lawfully congregate in South Africa.

''They pushed and shoved me and had a grenade in front of my face and pushed me to the back.