What was going on when I was born?

Moscow rejected a U.S. offer to join in talks on banning weapons in outer space, proposed by Moscow this weekend, if other subjects were discussed as well. Soviet leaders said the United States response was ''totally unsatisfactory,'' but the offer to open negotiations in September to prevent ''the militarization of outer space'' remained open. (Page A1, Column 6.) Moscow's rejection was regretted by the Reagan Administration, but it restated its willingness '' to sit down with the Soviets at a meeting in September as the Soviets have proposed.'' The Administration said Moscow had misread the intention of its statement Friday. (A1:6.)

Neither rain nor fog nor gloom of night kept the Mets from playing yesterday, or from breaking their four- game losing streak, which they did by sweeping a doubleheader from the Atlanta Braves by 2-1 and 3-2. While 8,949 fans huddled in Shea Stadium, the Mets drew within one game of first place in the three-way race in the National League's East, and even supplied some touches of history. In the opening game, Ron Darling became the first rookie to win nine games this season, and the first Met starter to win six straight since Tom Seaver did it nine years ago. And in the second game, George Foster hit the 300th home run of his 13-year career. It was his 11th of the season, but his first in three weeks, and Foster for once heard cheering instead of booing as he became the 48th player in baseball history to reach 300.

Takeover fever moved many of the big gainers, and financial woes plagued most of the top losers in an otherwise weak second quarter on the nation's three major stock exchanges. The Dow Jones industrial average, which dropped to a 16-month low in mid-June, managed to close on Friday down just 3 percent from the start of the quarter. Of 4,325 stocks on the three big markets tracked by Media General Inc., however, 2,731 - or 63 percent - lost ground in the quarter. Of the combined top 10 gainers on the New York, American and over- the-counter stock markets, about half benefited from takeover offers or rumors, eight on the New York Stock Exchange alone.

In the second inning, Dan Petry threw a split-fingered fastball and Dave Winfield hit it to right field for a single. In the fourth inning, Petry threw a fastball, and Winfield singled to center. Petry tried a slider in the fifth, and Winfield singled to left. ''He got hits on three of the four pitches I throw,'' Petry, the 10-game winner with the Detroit Tigers, said in admiration. ''The next time up he probably would've gotten a hit on a curve.'' The next time up, Winfield lined a fastball from Doug Bair against the fence in left- center field for a two-run double. ''It was up and in, right where I wanted it,'' Bair explained. ''I threw him the same pitch in Detroit, and he popped it up. But this time he turned on it and got his bat out in front. On pitches like that, most hitters couldn't get their bat out in front.''

The search for intelligent life elsewhere in the universe, a quest that began 25 years ago, is about to enter a new era. The awesome task, which involves scanning hundreds of billions of stars, has so far yielded no clear evidence that life exists beyond Earth. But new discoveries bearing on the probabilities of other civilizations, and new methods of searching for them, are attracting the interest of scientists. Two observatories are now engaged full time in the search, and detectors millions of times more effective than any used before are scheduled to be put into operation this fall. These new experiments represent the first ''systematic search'' by physicists for intelligent life beyond Earth, Dr. Philip Morrison of the Massachusetts Institute of Technology said yesterday.

Thousands of weary and frustrated travelers were stranded at Kennedy International Airport yesterday as New Yorkers pumped out from a weekend deluge that dropped four to seven inches of rain on the metropolitan area. As the storm headed out to sea yesterday evening, flooding receded from highways, allowing motorists to reclaim their abandoned cars. Full residential power and subway service were restored, but the Long Island Rail Road said severe flooding would force suspension of all service today between Port Washington, L.I., and Bayside, Queens. Flights Diverted The heaviest rain fell in Queens, shutting Kennedy Airport for eight and a half hours Saturday and disrupting travel plans for thousands of passengers on the busy weekend before the Fourth of July.