What was going on when I was born?

A Defense Department spokesman said today that a United States Navy destroyer came close to a Soviet freighter off the Pacific coast of Nicaragua on Saturday and asked the vessel's destination and cargo. The spokesman said that as the destroyer, the Lynde McCormick, approached the merchant ship, the Aleksandr Ulyanov, at a point about 50 miles off the coast, the American captain hailed the Soviet captain on a bridge-to-bridge radio. The ships were no closer than three-quarters of a mile apart, the Pentagon said. According to the spokesman, the American captain asked the Russian to list his cargo and destination. The Russian, he said, replied that he was carrying trucks and other general merchandise and was bound for Corinto, a port 90 miles north of the Nicaraguan capital at Managua.

The Reagan Administration appears to have taken a calculated political gamble in its decision to join other major industrial nations in substantial intervention in foreign-exchange trading to try to guide the value of the dollar. Senior officials in the Administration said they remained convinced that transactions of this sort, if they were effective at all, had only a momentary impact on prices in the currency markets. Currency values, they believe, are determined by such basic factors as differences in the rate of growth in the money supplies of nations and by inflation among nations - not by the vicissitudes of day-to-day trading in world financial markets. Indeed, Larry Speakes, the White House spokesman, went out of his way yesterday to emphasize that ''there is no change'' in Washington's policy of intervening only when currency trading is ''disorderly.''

''I happen to be one who believes if it wasn't for women, us men would still be walking around in skin suits, carrying clubs.''

Subway riders, already suffering from a summer of poor service, will encounter a new delay beginning Monday when trains that run on the Manhattan Bridge are rerouted to make way for reconstruction work. The 74-year-old bridge over the East River has deteriorated dramatically over the last few years, in large measure because of the subway trains that rumble over the structure, according to state and local officials. Work on the bridge's four subway tracks will continue for about three months. During the first six weeks, the BMT's N and QB trains will be diverted; during the second six weeks, the IND's B and D trains will be diverted.

The Justice Department sued the General Motors Corporation today, charging that the company had sold 1980 X-model cars knowing they had hazardous brake defects. The department seeks to have the manufacturer recall and repair all 1.1 million of those cars and pay the Government $4 million in civil penalties. The suit, filed in Federal District Court here, accuses General Motors of trying to cover up the extent of the problem by providing false information to the National Highway Traffic Safety Administration. The suit further charges that company officials, under oath in some of the instances in the Government inquiry into the defects, gave answers ''they knew or should have known'' were false. A Justice Department spokesman, Brad Marman, said the department would not specify why it was not pursuing perjury charges.

With concern rising over the fighting in Chad, Pentagon and State Department spokesmen announced today that two Awacs reconnaissance planes had been flown to Egypt and several military advisers had been sent to Chad. The sophisticated radar planes, scheduled to take part in long-planned military exercises with the Egyptians, would be capable of surveying air activity over parts of Libya and Chad, the spokesmen noted. The United States has already condemned Libya for air attacks on Chad, the former French colony that is its southern neighbor. Today a shipment of antiaircraft missiles was delivered to Chad by the United States, and the State Department said ''a small number'' of American military advisers had arrived in Chad to train Government forces in the use of the missiles.

The Advertising column in Business Day Friday gave an incorrect date for the founding of the company that owns the Bank Leumi Trust Company. It was 1902.

The Big Three auto makers reported today that sales surged 37.1 percent in the last 10 days of July, continuing the recovery that has been pushing up sales sharply since April. The General Motors Corporation, the industry giant, said its 10-day sales rose 44.3 percent from last year, on a daily selling rate basis. The Chrylser Corporation, the No. 3 auto maker, said sales jumped 48.5 percent in the July 21-31 period, while at the Ford Motor Company, sales were up 17 percent. For all of July, sales by all the domestic manufacturers, including American Motors, Volkswagen of America and American Honda, totaled 576,864, up 39.6 percent.

Last August, the decline in interest rates helped ignite the stock market's most explosive rally ever. Nearly a year later, however, the pressure on those rates is upward and the market has turned jittery. In recent days, long-term rates have hit their highest levels since last autumn, propelled in part by the nation's economic recovery and in part by the huge Federal budget deficit. The dollar, meanwhile, has been pushed to new highs against many foreign currencies by investors anxious to take advantage of high interest yields in the United States. All this activity is making interest rates and their direction one of the hottest topics in the financial community. The New York Times interviewed 10 of the nation's leading economists for their views. Milton Friedman Economist Interest rates will rise as an inevitable consequence of the monetary explosion we've experienced over the past year. So far as the economy is concerned, rising rates will in the short run have no impact, because the recovery will continue vigorously through 1983. But it will threaten the continuation of the recovery in 1984. There is nothing that can reverse that trend at the moment; it's all in the pipeline. And there's nothing good that can be done, only a choice among bad things.

New York City has provided $7 million in police protection during the seven-week-old strike against the Consolidated Edison Company, according to police officials. They said it had been one of the city's most expensive labor disputes in terms of police protection in the last 25 years. Each day since the strike began June 18, roughly 600 police officers in three shifts have provided 24-hour protection at 56 Con Edison sites throughout the city, including all of the utility's generating plants. Overtime has accounted for more than half the cost.

The American Telephone and Telegraph Company and the United States Justice Department yesterday agreed to a Federal judge's final changes in their antitrust settlement, effectively clearing the way for A.T.& T. to dismantle the Bell system on Jan. 1. Among the changes American Telephone accepted, although reluctantly, was a requirement that it give up use of the name Bell, a name that has been connected with A.T.& T. almost since Alexander Graham Bell invented the telephone in 1876. As a result, millions of Americans who have referred to A.T.& T. as ''Ma Bell'' will no longer be legally correct. The Bell name will be used instead by Ma's offspring - the 22 local operating companies that are to be split from American Telephone on Jan. 1. They provide 80 percent of the nation's local telephone service.

International An American-Soviet sea contact about 50 miles off the Pacific coast of Nicaragua Saturday was confirmed by a Pentagon spokesman. He said that a Navy destroyer came close to a Soviet freighter and inquired about her destination and cargo and that the Soviet captain said he was carrying trucks and other general merchandise. (Page A1, Column 1.) A rise in the U.S. contribution to the International Monetary Fund totaling $8.4 billion was narrowly approved by the House. The 217-211 vote ended weeks of doubt that House leaders would muster enough votes for passage. The Senate has approved a similar bill, and the legislation must go to a House-Senate conference to resolve the differences. (A1:4-5.)