What was going on when I was born?

The Reagan Administration has told six Eastern European Governments that they cannot hope for improved relations with the United States if they continue to support Palestinian and other ''international terrorists,'' State Department officials said today. The Administration said that if the six nations wanted better relations, they would also have to stop carrying out espionage and seeking to evade American export laws. The officials said the warnings were given separately during meetings last month between R. Mark Palmer, Deputy Assistant Secretary of State for European Affairs, and the ambassadors of Bulgaria, Czechoslovakia, East Germany, Hungary, Poland and Rumania. The Administration originally planned to keep the warnings secret, but East European diplomats here and abroad discussed them with reporters. This led the officials to provide details.

Twenty-five transit police officers moved aboard a subway train that pulled into the Delancey Street station early yesterday with its horn blasting for help and arrested 22 youths on charges of robbing and terrorizing riders. The transit police, who had responded to a radio call for help from an officer aboard the train, described their intervention as ''posse-like'' and ''so instantaneous'' that none of the dozens of riders were injured and none of the suspects escaped. The officers lined up everyone who had been on the train against the station wall and sorted out, from nearly 100 youths, those accused of having taken part in the robberies. 'He's the Kid' ''That's the one, he took my money,'' a rider shouted at one youth.

Silicon Valley has become so crowded that one of its leading lights, the Intel Corporation, is suing the city of Santa Clara to slow the growth. Not far ahead, people worry, with just a trace of exaggeration, are traffic and pollution as bad as in Los Angeles. The slump in video games has cost hundreds of jobs, and the belated but immensely successful entry of the International Business Machines Corporation into personal computers has shattered some companies here. Envied Abroad Nevertheless, for all its well-publicized growing pains, Silicon Valley is booming. The valley, a narrow, roughly 25-mile strip from Palo Alto to San Jose, remains the envy of the industrial world. Many foreign leaders have made it an obligatory stop - President Francois Mitterrand of France visited recently - and its freewheeling spirit is held out as the missing ingredient in older, declining industries.

The State Health Commissioner reversed himself yesterday and said he would allow the Memorial Sloan-Kettering Cancer Center to acquire a nuclear magnetic resonance scanner. The scanner, one of the world's newest and most expensive pieces of medical technology, provides intricate images of the body's internal organs and analyzes its chemistry without harmful radiation. The Commissioner, Dr. David Axelrod, recommended two months ago that Memorial Sloan-Kettering be denied a scanner, known as an N.M.R., because it could use a similar machine at the nearby New York Hospital-Cornell Medical Center. He said duplicating the one at New York Hospital with another at Memorial would further inflate health costs.

Two Soviet-built planes of ''unknown nationality'' fired on a United States Army helicopter today while it was on an observation mission along the West German-Czechoslovak border, the Pentagon announced. The Cobra helicopter was not hit by the rocket and cannon fire, the Pentagon said, and returned safely to its home station in West Germany. The brief announcement, which gave only sketchy information, said the Army's European headquarters in Stuttgart, West Germany, was investigating the incident, which occurred at 2:40 P.M. Mission Called Routine Pentagon officials said it was not known whether the helicopter entered Czechoslovak airspace or whether the MIG's entered West German airspace. (In Munich, an official of West Germany's paramilitary border police said there were ''indications that the helicopter was several kilometers into Czechoslovak territory'' when it was fired on. A United States Army spokesman in Stuttgart declined to comment on the statement.)

Two United States Senators said today that Jose Napoleon Duarte, who is running for the presidency of El Salvador, told them he would seek negotiations with Nicaragua if he was elected. Reagan Administration officials have accused Nicaragua of seeking the overthrow of the Salvadoran Government through its support of rebels in that country. Much of the support is believed to be in the form of clandestine shipments of ammunition.

An explosion severely damaged the officers club at the Washington Navy Yard early this morning, and a group that said it opposed United States policy in Central America took responsibility. No one was in the building at the time. The Federal Bureau of Investigation said a group that called itself the Guerrilla Resistance Movement had taken responsibility for the bombing and had said it was ''in solidarity'' with the Farabundo Marti National Liberation Front, one of five leftist guerrilla groups fighting Government forces in El Salvador's civil war. The liberation front itself, often referred to as the F.M.L.N., denied any connection with the bombing. A spokesman in Washington, Francisco Altschul, said the F.M.L.N and the Frente Democratico Revolucionario, or F.D.R., the political arm of the guerrilla movement, ''categorically denies any involvement or responsibility in today's bombing of a U.S. Navy facility in Washington or in any other similar incident in the U.S.''

Nicaraguan Government troops supported by aerial bombing have retaken this remote jungle outpost from Costa Rican-based rebels. But they are in control of a town that no longer exists. About 500 insurgents, led by Eden Pastora Gomez, a hero from the days of Nicaragua's Sandinista revolution, attacked the military garrison here on April 10 and took it after three days of fighting during which at least 15 Sandinista defenders were killed. Mr. Pastora said that he intended to drive northward through the Mosquito Coast toward the provincial capital of Bluefields and that he would establish a provisional government in the area within 90 days. Forced to Retreat The Sandinista counterattack came quickly, however, and Mr. Pastora was forced to retreat into the jungle. In Managua, Government officials charged that the rebels were regrouping at camps inside Costa Rica, but Mr. Pastora's allies in the Costa Rican capital said he was still prowling near San Juan del Norte and might strike again soon.

If the Soviet Union and its Warsaw Pact allies decided to go to war, one of the first people to have a hint of impending hostilities might be Col. Roland Lajoie. The strapping Russian-speaking American soldier, a former Army attache in Moscow, leads one of the most secrecy-shrouded elite units in the United States military: a 14-man team that prowls East Germany conducting what amounts to legal espionage. In Opel sedans packed with telescopes, infrared cameras and listening devices, the colonel's Soviet counterparts do the same in West Germany. The city of Berlin reposes, in legal terms, on a crazy quilt of documents concluded from 1944 onward between the United States, Britain, the Soviet Union and France. Allied in the struggle to defeat Nazi Germany, the four countries at the end of World War II carved up the defeated nation into zones of occupation.

The Warsaw Pact has again demanded that the North Atlantic Treaty Organization halt deployment of nuclear missiles in Western Europe and said the bloc's members ''insist'' the program be stopped as a condition for resuming arms limitation talks. A communique issued today by the seven Warsaw Pact Foreign Ministers, who ended a two-day meeting here, though repeating the Soviet bloc's position, contained some of the strongest language to date on the bloc's stand on resuming the Geneva arms talks. ''The meeting's participants pointed,'' the communique said, ''to the great responsibility of the states on whose territory the deployment of medium-range nuclear missiles has started or is being planned, responsibility for the fate of their own and all European peoples.

-- The Government said today that it had received a secret Libyan response to its conditions for ending the four-day-old police siege of the Libyan Embassy here. It said the British Ambassador in Libya was being instructed on how to pursue negotiations. But officials here and reports from Libya gave no indication that there had been progress toward an agreement.

Twenty-three people were wounded tonight, one seriously, when a bomb exploded in an unclaimed baggage section inside Heathrow Airport. There was no immediate indication of who might be responsible for the bombing. Late tonight Commander William Hucklesby, head of Scotland Yard's anti-terrorist branch, said the bomb contained two pounds of commercial or military explosive. No warnings were given before the attack and no person or group had so far taken responsibility, he said.