What was going on when I was born?

Twenty years ago today, President John F. Kennedy publicly demanded that the Soviet Union remove its missiles from Cuba or else. And for 13 days, until agreement on their removal was reached, he thought that the chances of nuclear war were 1 in 3 or even. ''Above all, the Cuban missile crisis is a vivid reminder that, unless the superpowers act very carefully, they can set off a chain reaction leading to nuclear war,'' Graham T. Allison, dean of the John F. Kennedy School of Government at Harvard, remarked recently. For 20 years, the middle course charted by Mr. Kennedy to bring about the withdrawal of the missiles - neither direct military attack nor words alone - has served as a model to his successors on how to handle crises. At the time, this middle way was generally judged a brilliant success.

More gains were announced today for the political arm of the outlawed Provisional Irish Republican Army in Wednesday's elections in Northern Ireland, causing widespread private expressions of dismay among officials in London. Tabulation of the votes, while not yet complete, showed that the I.R.A.'s political organization, Sinn Fein, had picked up two more seats, for a total of five, in the 78-member assembly. This showing was widely regarded as an important psychological victory for the party, which entered 12 candidates, all in urban areas where Roman Catholics are concentrated, and campaigned on a slogan of ''A ballot in one hand and a gun in the other.''

The Essex County Prosecutor said today that he would move for dismissal of a misconduct charge against Mayor Kenneth A. Gibson. He had been accused of creating a ''no show'' job for a former City Councilman. On Thursday, a Superior Court judge declared a mistrial on the charge after a jury failed to reach a verdict. The jury acquitted Mr. Gibson of a conspiracy charge in connection with the job for the former Councilman.

A judge today ordered a hospital to discontinue life-sustaining treatments for a 41-year-old diabetic at his request, and within an hour the man died. The man, Peter Cinque of Lynbrook, died in the intensive-care unit of Lydia E. Hall Hospital in Freeport, L.I., at about 5 P.M. In his order, Justice Arthur D. Spatt of State Supreme Court had directed Mr. Cinque's doctors to honor his request to halt his dialysis treatments. ''In this state, there is no statute prohibiting a patient from declining medical treatment or a doctor from honoring a patient's decision,'' Justice Spatt said. ''The court finds Peter's decision was based on a compelling desire to escape the grievous pain and suffering.''

King Hassan II of Morocco met with President Reagan today and said that ''peace and coexistence'' in the Middle East could be achieved on the basis of American and Arab proposals and United Nations Security Council resolutions. The King, the leader of an Arab League delegation, did not specifically define what he meant by ''coexistence,'' or mention Israel. But a senior State Department official said later that the King's choice of words was important. In the private discussions, the official said, ''it was well understood that we were talking about a state called Israel and peace negotiations, the terms, modalities for negotiations.''

Laws that empower both Houses of Congress, acting together, to veto Federal agency rules were held unconstitutional today. The ruling was made by eight Federal appeals court judges, who acted unanimously. The ruling came in an uncharacteristically brief, unsigned opinion by the United States Court of Appeals for the District of Columbia Circuit. It struck down the so-called legislative veto of a Federal Trade Commission rule requiring used-car dealers to disclose major defects and other information to buyers.

Five key members of the political branch of El Salvador's leftist opposition were seized in the capital this week, political sources and human rights groups here said today. The whereabouts of the five, who were said to have been abducted by heavily armed men in civilian dress, remained unknown today. Relatives and human rights groups, concerned for their safety, appealed to the United States and Salvadoran Governments to seek their release. One source familiar with the left said the five men are the core of the Democratic Revolutionary Front affiliates remaining in the country. Most leaders of the front are in exile.

Prime Minister Pierre Elliott Trudeau went on national television three times this week to dramatize the depth of his nation's economic problems and to urge Canadians to work together to solve them. ''In our country, as we face winter, men and women - almost a million and a half of them - are without jobs,'' he said in the third 15-minute prime-time broadcast Thursday night. ''Many more live with the worry that your jobs will be next.'' Despite Mr. Trudeau's warning that Canada is ''in trouble,'' he offered no new policy directons, instead urging adherence to the Government's existing voluntary restraint program. In addition, he blamed the worldwide economic downturn for many of Canada's difficulties.

President Francois Mitterrand said today that France was taking steps to consult with West Germany about nuclear strategy and that the two countries had decided to seek a common military doctrine in Western Europe. At a news conference on the second day of their talks, Chancellor Helmut Kohl and President Mitterrand announced the formation of a coordinating committee of their foreign and defense ministries that will meet between the heads of state conferences that take place every six months. ''Questions of security policy took up a very large part of our talks,'' Mr. Kohl said in a statement. ''We have, for the first time in 19 years, activated an agreement of the French-German friendship treaty which explicitly points to the development of a common security policy.''

All-night talks to decide on a successor to Prime Minister Zenko Suzuki broke down here at dawn today amid signs of a widening split in the ruling Liberal Democratic Party over the succession.

A wave of vandalism and break-ins has strirred fears among Western diplomats here of a campaign of harassment against representatives of countries seen as unfriendly to Poland's martial-law administration. The embassies of both the United States and France, the nations that have borne the brunt of the incidents, have filed formal complaints with the Polish Foreign Ministry. The incidents, which began last summer and have markedly increased in the last week, include mysterious burglaries at the houses of diplomats and other foreigners and the splashing of paint on cars and buildings. Pink Paint on French Embassy On Monday night bottles of pink paint were thrown against the walls of the French Embassy and on a car belonging to the French cultural center. On Wednesday night three cars at the United States Embassy - clearly identifiable, as are all diplomatic vehicles, by their special plates - were smeared with yellow paint and a fourth had its tires slashed outside an apartment block used by embassy personnel. Two offices housing agriculture and trade missions were also daubed with painted swastikas and the letters P L O.

Armando Valladares, the Cuban poet who spent 22 years in prison for criticizing Fidel Castro and was freed after the personal intervention of President Francois Mitterrand, was reunited with his wife today on his arrival in Paris. The tall, emaciated 44-year-old writer stepped slowly down from a special French Government jetliner that picked him up in Madrid early today. The poet flew to Spain aboard a Soviet IL-62 jetliner that left Havana Thursday.