What was going on when I was born?

A team of Federal scientists says it has detected an overall warming trend in the earth's atmosphere extending back to the year 1880. They regard this as evidence of the validity of the ''greenhouse'' effect, in which increasing amounts of carbon dioxide cause steady temperature increases. The seven atmospheric scientists predict a global warming of ''almost unprecedented magnitude'' in the next century. It might even be sufficient to melt and dislodge the ice cover of West Antarctica, they say, eventually leading to a worldwide rise of 15 to 20 feet in the sea level. In that case, they say, it would ''flood 25 percent of Louisiana and Florida, 10 percent of New Jersey and many other lowlands throughout the world'' within a century or less.

Senator Harrison A. Williams Jr. said today that he had learned that the special counsel for the Senate Select Committee on Ethics had recommended his expulsion from the Senate for his activities during the Abscam undercover investigation. The New Jersey Democrat, now in his 23d year in the Senate, said in a telephone interview that he had obtained his information from reliable sources. He also said that he had considered resigning, but that ''at this point my conscience tells me to stick and fight.'' ''You know,'' he added, ''it's just not right. I made foolish, meaningless mistakes, but I did not violate my trust or the law.'' The three Republicans and three Democrats on the ethics committee are scheduled to hold a closed meeting Monday to consider the report of the special counsel, Robert S. Bennett of Washington, who conducted the committee's inquiry. Sources close to the inquiry confirmed Mr. Bennett's recommendations, but declined to predict whether the panel would support them. Under committee rules, four votes are needed for a disciplinary resolution to be sent to the Senate floor.

Gasoline prices in the United States are expected to remain generally stable and possibly dip slightly over the next few months because of the failure yesterday of the oil ministers of the Organization of Petroleum Exporting Countries to agree on a uniform pricing policy. The result is particularly good news in view of the widespread expectation before and during the ministers' meeting in Geneva that OPEC would agree to a range of prices between $34 and $37 a barrel, rather than the current $32 to $40. Had the new range been adopted, with its $34 minimum price, it would have increased gasoline prices in the United States, many of which are tied to the $32 price that Saudi Arabia charges for its basic crude. OPEC's indecisiveness thus, in effect, saved American drivers 3 cents or more a gallon, oil analysts calculate. 'Good News for the Consumer' ''Obviously this is good news for the consumer,'' said John H. Lichtblau, executive director of the Petroleum Industry Research Foundation.

A three-day meeting of OPEC oil ministers ended today in failure to reach agreement on a new, lower range of prices.But Saudi Arabia, which accounts for one-fifth of the West's oil production, said it would maintain its price of $32 a barrel through 1982. The OPEC meeting, which many participants considered the most divisive and difficult in the group's 21-year history, appears to have produced a decisive victory for the Saudi policy of applying pressure to reduce world oil prices. One result of the meeting is that prices of petroleum products in the United States probably will remain stable or perhaps dip slightly. The price of gasoline at American service stations could drop by 3 cents or more a gallon from current averages of $1.34 to $1.41 a gallon, industry analysts calculate.

Pentagon officials gave a detailed report today on Wednesday's dogfight over the Gulf of Sidra to support the United States contention that American pilots shot down two Libyan planes only after being fired at first. The account included exerpts that the officials said were from intercepted radio communications by the lead Libyan pilot. According to one of the excerpts, the pilot said, in Arabic, ''I am preparing to fire,'' and, a moment later, ''I have fired.'' The officials said these statements were translated after the incident and were not known to the American pilots at the time of the encounter.

Leaders of two key Congressional military committees told President Reagan today that they opposed Defense Secretary Caspar W. Weinberger's proposals for an air-based MX missile and for a more advanced ''common missile'' to be used by both the Air Force and Navy. Senator John Tower, Republican of Texas, and Representative William L. Dickinson, Republican of Alabama, said after a luncheon meeting with Mr. Reagan at the Century Plaza Hotel here that they did not expect a White House decision on the matter for several weeks. But their two-hour meeting with the vacationing President pointed up the sensitive politics of this military policy decision, which has stirred conflicting views within the Cabinet and caused deep unhappiness among Mr. Reagan's supporters in Nevada and Utah. Doubts in the Campaign In the Presidential campaign, Mr. Reagan indicated that he had grave doubts about the so-called ''racetrack'' method of basing the MX missiles in those two states. The method would involve shuffling 200 missiles on motor carriers among 4,600 silos. The silos and their connecting track would be built on a huge Federal reservation whose creation is opposed by many Utah and Nevada citizens, including leaders of the Mormon Church and other strong Reagan allies, as a blight on their area.

The price of military equipment, including Awacs planes, that Saudi Arabia wants to buy from the United States has risen to $8.5 billion, Administration officials said today. This is nearly $4 billion more than the rough price estimates Administration officials gave to Congressmen this spring. The increase brings the price of the arms sale, of which President Reagan will formally notify Congress on Monday, considerably closer to the $12 billion the United States paid to import crude oil from Saudi Arabia last year. The proposed sale, which Congress can veto, is expected to cause a foreign policy debate that could turn into a major challenge to President Reagan. The price of the arms sale gives increased weight to an argument that in part it should be approved because it helps to ''recycle petrodollars.''

As waters from the second major flood in a month receded in Sichuan Province this week, Chinese officials and scientists disclosed that deforestation in China's most populous province was a major cause of flood devastation there. Tan Qilong, Sichuan's Communist Party secretary, said this week that the indiscriminate cutting of trees over the past three decades had denuded most of the province's watershed areas in the upper reaches of the Yangtze River. This had allowed the water from normal torrential summer downpours to flow unchecked into tributary river systems, he said.

Each week, Le Nouvel Observateur chooses a luminary of the Parisian intellectual or artistic world to set out his or her choices among the cultural events of the succeeding week. One week last May it chose Arthur A. Hartman. That the newspaper, a pillar of the French left, should pick the American Ambassador to tell Parisian intellectuals what to go see or hear was nothing short of remarkable. Not since Benjamin Franklin has an American envoy to France been given such public recognition for his culture.

Tran Thi Yen, her husband and their three young children fled from Vietnam because, she said, ''we wanted to have a future for the children.'' Three other young women from southern Vietnam nodded sympathetically, as if to say that they had escaped for the same reason. Today, three of the four are widows, and 9 of their 11 children are dead. How many people died on their boat, how many families were lost without survivors, will never be known. The 16 who made it as far as a refugee camp here know only that there were more than 70 aboard when their boat left the southern fishing port of Rach Gia on June 28.

Polish news organizations eased their attacks today on the independent union Solidarity, but tensions persisted between the two sides in the wake of a nationwide printers' strike. In the northern city of Olsztyn, printers continued their takeover of the presses of the local newspaper, Glos Olsztynski, demanding that the state television retract an allegation that they had forcibly prevented others from working during the 48-hour strike, which ended yesterday. Television did not broadcast the retraction, prompting the Olsztyn printers to say they would remain and shut down the newspaper indefinitely. They issued many other demands, including one asking for investigations of officials who have been dismissed for corruption.

In a defeat for the Protestant establishment of Northern Ireland, another hard-line supporter of the Irish Republican Army has been elected to the British Parliament. Owen Carron, 28 years old, an unemployed high school teacher, was declared the winner today in a by-election in the rural southwest of the province. He will succeed Robert Sands, who won the seat last April while he was on a hunger strike in Maze Prison outside Belfast. He starved to death a few weeks after his election.