What was going on when I was born?

Despite demonstrations at New York City's main post office and in other major cities across the country yesterday, thousands of 19- and 20-year-old men quietly signed up on the first day of registration for a possible military draft.

LONDON, July 21 A group of oil companies drilling in the North Sea about 70 miles off the coast of Norway has discovered what may be one of the world's largest natural gas fields.

FOR 25 days my sleep patterns were the focus of a rigorous experiment at Montefiore Hospital, where I was a research sub ject. Since leaving the chronophysiology laboratory there, it has taken me 10 days to regain my normal sleep habits, and I still find myself hypersensitive, unable to make quick decisions. I have no reserves of energy.

PARIS, July 21 A former Prime Minister of Syria and opponent of President Hafez al-Assad was assassinated today as he was about to enter the office of the magazine that he edited here.

BROOKSTON, Ind. AFTER a night in the damp chill of a mosquito-ridden pond waiting for an uncooperative population of bullfrogs to go a-courtin', it's easy to see why so little was known until recently about the intriguing behavior of this nocturnal animal whose legs are served for dinner and whose mating choruses are lullabies on summer nights.

USING a variety of inventive approaches to collect and examine meteoritic particles from the air, sea and land, geolo gists now estimate that 100 tons of cosmic material fall to Earth every day.

"They were holding the Brooklyn Bridge, it was theirs for three or four hours," said Mark Segall, a Brooklyn bicyclist who was attacked, robbed and held prisoner on the bridge's walkway by four muggers.

MINNEAPOLIS When the Control Data Corporation recently took the wraps off its ultra-fast, highly precise Cyber 205 computer, it signaled the beginning of a battle in the rarefied and somewhat serene world of supercomputers.

A Suffolk County grand jury has concluded in a report that residents of the county's Southwest Sewer District were "recklessly, if not deliberately deceived" in 1969 to approve the $932 million project, but the panel handed up no new indictments in the case.

E.I. du Pont de Nemours Company, confirming what has been nearly an across-the-board earnings decline for chemical companies in the second quarter, reported yesterday that net income in the latest period tumbled 24 percent as sales edged 5.2 percent higher.

The Morgan Guaranty Trust Company and the Bankers Trust Company yesterday became the first major banks to reduce their prime lending rates to 11 percent, the lowest level since November 1978.