What was going on when I was born?

The smallest of the six living Frustaci septuplets, a boy called Baby F, died early today after his lungs failed. With the boy's death at 12:34 A.M., three boys and two girls survive from the largest multiple birth in American history. The baby born last, a girl known as Baby G, was stillborn. Their mother, Patti Frustaci, a 30-year-old teacher who had taken a fertility drug, remained at St. Joseph Hospital, where the babies were delivered by Caesarean section. Tes Pane, the nursing supervisor overseeing her care, described Mrs. Frustaci as exhausted and emotionally distraught. The babies are in the adjacent Children's Hospital of Orange County.

Sri Lanka's President said today that he intended to establish martial-law courts to deal with what he called ''a breakdown of law and order.'' The President, J. R. Jayewardene, under pressure from the ethnic Sinhalese majority to take more decisive action against militant Tamil separatists, also said he was about to embark on a political experiment in which he plans to make every Member of Parliament directly responsible for the security of his or her electorate. With that responsibility, the President said in an interview, will come the right to arm local communities. 'Give Us Arms' ''They are complaining, all of them,'' the President, 78 years old, said of the legislators. ''My people are saying: 'The terrorist comes and shoots us and goes off. We have no arms. We have no nothing. So give us arms.' ''

President Reagan said today that the Democratic budget for 1986, by permitting no increase in the military budget, would place the nation's defense at risk. . The budget the Democratic-controlled House of Representatives approved by a wide margin Thursday is loaded with unacceptable ''phantom'' savings and fails adequately to address the ''fundamental problem of unbridled domestic spending,'' Mr. Reagan asserted. In a speech before the National Association of Manufacturers, the President also offered the opening salvo in a major Administration drive to gain Congressional approval of a plan to simplify the Federal income tax. 'Simpler, Fairer, Streamlined' Although he did not disclose details of the proposal, which he will unveil in a nationally televised address Tuesday evening, Mr. Reagan said the time had come for replacing a system whose complexity makes it ''ripe for abuse.'' ''We propose to replace a tax system that is almost universally regarded as needlessly complicated and unfair with a simpler, fairer, more streamlined model,'' Mr. Reagan said.

A New York City physician, on the run for two years since his indictment for treating suspects in the Brink's robbery and killings in Rockland County, has been arrested, the Federal Bureau of Investigation announced yesterday. The doctor, Alan Berkman, who is 39 years old, was apprehended Thursday night by F.B.I. agents in Bucks County, Pa., near Philadelphia. Dr. Berkman was arrested after his car was forced to the side of a road, John L. Hogan, special agent in charge of the F.B.I. bureau in Philadelphia, said. Mr. Hogan said the doctor had a loaded revolver in his lap and wore a woman's brown, curly wig. Arrested with Dr. Berkman was Elizabeth Duke, 44, of Austin, Tex. Mr. Hogan said Dr. Berkman and Miss Duke were members of the May 19 Communist Movement, which he described as a Marxist organization dedicated to overthrowing the United States Government.

At 38, Douglas Kreeger walks around the city, a merchant without a store, trying to turn off the instincts that made him successful for 13 years. ''It's like deprogramming my head after all that time,'' he said. ''I see an advertisement, or some merchandise, and I start thinking how I would promote it,'' Mr. Kreeger said. ''Or I see some real estate, and I tell myself what a great location it is.'' In March 1984, he sold Kreeger & Sons, the camping and backpacking chain he founded, to the Dutch-owned Amcena Corporation. The chain, whose merchandise and clothing had a relaxed and authentic outdoor feel that even competitors admired, had developed a devoted following.

The battle for control of three Palestinian refugee camps grew more intense today, with Shiite Moslem militiamen and Lebanese Army troops flattening buildings with tanks and bulldozers, and Palestinian defenders mounting ambushes from tunnels. The latest phase in the fighting followed an unsuccessful attempt to halt six days of gun battles in and around the camps, actually cinder-block shantytowns, known as Sabra, Shatila and Burj al Brajneh. According to police reports, 250 people have been killed and 900 wounded since Sunday. Many of those killed and wounded have been noncombatant civilians.

Robert A. Rowland resigned today as head of the Occupational Safety and Health Administration, saying his ''mission has been accomplished.'' Soon afterward the Office of Government Ethics said it had found no conflict of interest in Mr. Rowland's participation in regulatory matters affecting companies in which he owned a total of more than $1 million in stock. Mr. Rowland said in a statement that he was ''pleased to learn'' that the ethics office had ''given me a clean bill of health.'' 'Baseless' Allegations ''As I said in the past,'' Mr. Rowland said, ''the allegations against me of possible conflict of interest were baseless and without merit.''

Anton Koslov traveled from New York City to Ottawa recently to tell anyone who would listen about his father. The young immigrant from the Soviet Union explained that his father, Lev Timofeyev, had been arrested in Moscow last March and charged with ''anti-Soviet agitation and propaganda'' after some of his writings were published abroad. And Juta Gallus-Schmidt came from Stuttgart to plead for her children, Claudia and Beate. Mrs. Gallus-Schmidt and her husband served two years in prison for trying to flee East Germany until West Germany paid to get them out, she said, but East Germany kept her children. People telling these and other poignant stories of heartbreak and separation descended on Ottawa when a six-week conference of experts on human rights opened May 7.

The Reagan Administration said today that it was seeking a full explanation from the South African Government about the military mission into Angola. A State Department spokesman, Edward P. Djerejian, said the United States had no knowledge of any possible South African military operation in Cabinda province until the Angolan and South African announcements. ''We have made known to the South African Government our deep displeasure over Tuesday night's incident at Cabinda, and we are seeking a full explanation from the South African government,'' Mr. Djerejian said. He declined to respond to questions about whether the United States knew about South African intelligence teams in Angola.

South Africa today requested an urgent meeting with Angola to discuss the return of South African soldiers reported killed or taken prisoner in what appears to have been an abortive covert mission in northern Angola. There was no immediate word of an Angolan reply. On Thursday, South Africa acknowledged for the first time that it had sent troops into northern Angola, saying that they were on a spy mission.

The police broke up demonstrations today by hundreds of youths at five universities in support of 60 students occupying a United States Government office here. Witnesses said some demonstrators hurled gasoline-filled bottles at the police, who responded with tear gas. The takeover at the four-story United States Mission building continued tonight, with the 60 students still barricaded in the second-floor library while American officials spent a second day trying to persuade the protesters to leave.

A Paris-based Nazi hunter led a small demonstration here today to demand the arrest and extradition of the Auschwitz death-camp doctor, Josef Mengele, who she says is being protected by Paraguay's rightist regime. The Nazi hunter, Beate Klarsfeld, who with her husband, Serge, played a key role in getting Klaus Barbie, the war criminal, extradited from Bolivia to France in 1983, said she was convinced that Dr. Mengele is in Paraguay. ''If you think logically, there is no where else that he could be,'' she said. ''If he left, the police must know, it must be in their files.''