What was going on when I was born?

The Algerian intermediaries in the hostage crisis flew home today to discuss with their leaders the latest American proposal before going on to Iran for what could be a decisive round of talks. With three weeks remaining in office, Carter Administration officials again contended that an American reformulation of previous proposals offered Iran a practical way to resolve the 14-month-old crisis if there was political will to do so. Meanwhile, the Iranian radio, in an unattributed commentary, broadcast a new threat to put the hostages on trial and possibly execute them. ''It is natural that according to Islamic laws, the trial of the hostages not only might lead to their execution, being guilty of spying, but even more important, it will expose the unwarranted interference of imperialism in other countries,'' the broadcast said.

The development of a promising screening test for carriers of cystic fibrosis, the most common lethal inherited disease of white Americans, was reported yesterday by medical scientists in Boston. Children born with the condition have trouble clearing mucus from their airways, become prey to infections of the respiratory tract and often die in their late teens or early 20's, although in rare instances they survive much longer. It is estimated that one in every 1,600 to 2,500 babies born alive in the United States is afflicted with cystic fibrosis. The disease is rare in racial groups other than whites. Sickle cell anemia, which affects blacks almost entirely, is 4.5 times more prevalent among blacks than cystic fibrosis is among whites, according to the Merck Manual.

After the most tortured census in American history, plagued by bitter lawsuits, the Census Bureau officially certified the 1980 population count of the states today and reported it to President Carter only hours before the legal deadline. It was able to do so only after the Supreme Court last night overturned an order by a lower Federal court that had blocked the certification, pending the Government's appeal of a successful assertion by New York City that its count should be adjusted to make up for New Yorkers overlooked by census takers. The final national population count, released today at ceremonies at the Commerce Department, of which the Census Bureau is a part, was 226,504,825. This was 11.4 percent above the 1970 count of 203,302,031 and somewhat higher than ''preliminary'' figures released earlier this month.

Corruption in state and local government in Massachusetts was so pervasive in the 1960's and 1970's that it became ''a way of life,'' a special state investigating commission concluded today after two and a half years of study. In one of the most sweeping indictments ever made of the conduct of a state government, the commission said that bribery, extortion, tax evasion, illegal campaign contributions and the laundering of money to disguise its origins were commonplace and that ''there is a tacit understanding between public servants and private professionals that this is how business is done in Massachusetts.'' The Special Commission Concerning State and County Buildings, set up in 1978 after the state's worst corruption scandal, said in its 2,500-page report that blame could not be narrowed down to a handful of individuals. 'Broad and Pervasive Pattern' ''It was not a matter of a few crooks, some bad apples which spoil the lot,'' the commission said. ''The pattern is too broad and pervasive for that easy excuse. At those crucial points where money and power came together, the system has been rotten.''

The Government index designed to forecast future economic trends rose significantly in November, the Commerce Department reported today, indicating that the weakness forecast by many economists is still not in sight. The 1.2 percent increase in the index of leading indicators - the sixth consecutive monthly rise - was viewed as confirmation that the economy was continuing to perform more strongly than the analysts expected. Although Government and private economists said that they still expected a weakening early in 1981, the addition of this latest statistic to a variety of similarly encouraging figures released in recent days made them less certain of their forecasts. Wonder 'About the Odds' ''It does make you wonder a little more about the odds we put on a decline in activity in the first quarter of next year,'' said Albert H. Cox Jr., president of Merrill Lynch Economics.

Associated Press and United Press International President Carter yesterday as he returned to Washington from Camp David, the Presidential retreat in Maryland. Today Mr. Carter goes to New Orleans to watch the Sugar Bowl. President-elect Ronald Reagan and his wife, Nancy, traveled to Palm Springs, Calif., from Los Angeles for a two-day holiday.

Lieut. Gov. William Atchison O'Neill was sworn in today as Connecticut's 84th Governor in a brief and somber ceremony at the State Capitol, a few blocks from the hospital where Ella T. Grasso is fighting the cancer that forced her to resign as Governor. Mr. O'Neill, 50 years old, of East Hampton, who has been involved in state and local Democratic politics for a quarter-century, paid tribute to Mrs. Grasso's courage in brief remarks after taking the oath of office from Chief Justice John P. Cotter of the State Supreme Court. Mr. O'Neill said: ''And I pledge to you, Ella Grasso, and indeed to the people of the State of Connecticut, that I will do my utmost to humbly guide this state in a manner that I think Ella Grasso would have, had she been able to continue during the next two-year period. To do anything less would be a travesty of justice.''

Marshall McLuhan, the communications theorist who taught that ''the medium is the message,'' died yesterday in his sleep at his Toronto home, his family reported. He was 69 years old. ''Most people are alive in an earlier time, but you must be alive in our own time,'' Mr. McLuhan once said. Born in what he considered an age of information, Mr. McLuhan strove to understand and explain the electronic media, which he believed were shaping people in ways they hardly suspected. Meaning of Oft-Quoted Maxim He had a penchant for aphorisms - as well as a weakness for puns - and he summed up his views on the effects of media in the maxim ''the medium is the message.'' By this he meant that the way we acquire information affects us more than the information itself.

''I am not really familiar with what Professor Faurisson says, but I will defend to the death his right to say it'': this, approximately, is the line that the American linguist Noam Chomsky is sticking to in his slanging match with a clutch of French intellectuals, academics and journalists. Le Monde, Liberation and other newspapers have been full of interviews with Professor Chomsky, of letters or portions of letters or reports of letters from Professor Chomsky to friends, of articles attacking him and other articles merely questioning his judgment. The whole thing has turned into an ''affaire,'' which in the French intellectual world is the equivalent of a tempest in a teapot, if you are inside the teapot. The affair involves Robert Faurisson, a lecturer in classical and modern literature, now suspended, at the University of Lyons, who for the past few years has been advancing the contention that there were no Nazi death camps in World War II.

Just after noon each day in offices around Peking, many employees carefully clear off their desks and spread bedrolls over them. They are preparing for one of the most important and satisfying rituals of Chinese life, the long midday nap, or xiuxi. Few Chinese would consider doing anything other than sleep during their siesta, which lasts two hours in the winter and up to three hours in the summer. Lunch is eaten on office time before noon. Shopping is accomplished during extended breaks in the morning and afternoon. An American engineer who visited an oil rig in the South China Sea was astounded to find that the crewmen stopped drilling when lunchtime approached, then turned off all the machinery and went to sleep. Since it costs $50,000 a day to run an offshore rig and since stopping the drill can cause technical troubles, Western crews work 24 hours a day, he said.

Wearing aviator sunglasses, black hair curling from under his green baseball-style cap and a black collapsible-stock automatic rifle hanging from a strap around his neck, the short rotund man began by justifying his authority with a quotation from the Letter of St. Paul to the Romans. Beneath a tree on a wind-blown hilltop, he followed with a discourse about the social and economic injustices in El Salvador, quoting from Mao Zedong and telling a parable about two boxers: ''One is big, strong and blond; the other short, weak and black. The people always support the short black one.'' It was his way of explaining why he says the international community supports the guerrillas.

The Government of Prime Minister Adolfo Suarez appeared today to have made a major breakthrough in the tortuous negotiations to confer real governing powers on the fledgling homerule authority in the Basque region. A Cabinet decision to restore taxation powers once enjoyed by the Basques, and the move a week ago to give impetus to the formation of a Basque police force, cleared the most important unresolved issues that had been pending between Mr. Suarez and Carlos Garaicoetxea, the moderate president of the regional government. The national Treasury Minister, Jaime Garcia Anoveros, who conducted the marathon talks on the key taxation question, called the accord, perhaps a bit grandly, ''the last thing that remained to be overcome to end finally the consequences of the civil war.''