What was going on when I was born?

President Reagan said today that Laos had agreed to allow United States officials to excavate a site to search for the remains of 13 American servicemen whose plane crashed there nearly 12 years ago. Mr. Reagan made the disclosure during a ceremony at the White House in honor of National P.O.W./M.I.A. Recognition Day. At the ceremony, the President said the Administration was determined to recover the remains and press for information on 2,489 Americans unaccounted for from the Vietnam War, as well as 8,177 from the Korean War. About 600 of the 2,489 were reported dead or missing in Laos. The Vientiane Government met with American officials last year and allowed a technical team to visit the crash site, near the city of Pakse.

Officials of the Miss America Pageant voted unanimously today to ask the reigning queen, Vanessa Williams, to resign, after they learned that she had posed for nude pictures before her selection for the title. The pictures will be published in the September issue of Penthouse magazine. Albert A. Marks Jr., executive director of the pageant, said at a news conference here that the committee had decided it had no choice but to recall her crown. For her to ''remain as Miss America would seriously jeopardize and irrevocably damage the entire Miss America Pageant program,'' he said. He said she would have 72 hours to decide whether to resign. Her lawyer told pageant officials that Miss Williams would announce her decision at a news conference on Monday, Mr. Marks said.

Laos agreed to allow U.S. officials to excavate a site to search for the remains of 13 American servicemen whose plane crashed there nearly 12 years ago, President Reagan said. Mr. Reagan made the announcement at a White House ceremony observing National P.O.W./M.I.A. Recognition Day. He affirmed his Administration's determination to recover the remains and press for information on 2,489 Americans unaccounted for from the Vietnam War and 8,177 from the Korean War. (Page 1, Column 4.) Relatives of missing Guatamalans have started to band together in an effort to find their relatives and end the many unsolved disappearances. Such organizations have long been active in other Latin American countries where kidnapping has beome a favorite way of disposing of real or imagined enemies. (2:1.)

The wife of one of Mexico's wealthiest citizens was kidnapped at gunpoint Thursday night from the Sheraton-Washington Hotel, the Federal Bureau of Investigation said today. The woman, Edith Rosenkranz, was in the hotel to play in a national bridge championship with her husband, George, who founded the Syntex Corporation and helped develop the first birth-control pill. Officials of the F.B.I. and the Washington police refused to say whether a ransom demand had been received. Mr. Rosenkranz was not available for comment. (A woman answering the phone at the Rosenkranz residence in Mexico City and identifying herself as a relative said the family had not received a ransom demand, United Press International reported.)

The two-year drought that has caused a loss estimated at $1 billion to Texas farmers and ranchers is now drying up the state's cities and crippling vacation resorts. Sixty-seven cities, including San Antonio, the state's third largest, and Austin, the capital, have imposed voluntary or mandatory restrictions on the use of municipal water. At resorts along fresh-water streams and lakes, tourist business is as low as the water levels. The drought in Texas threatens to become the worst since the 1950's. Lakes, reservoirs and aquifers across the center of the state are far below normal, and by this week 67 cities had imposed voluntary or mandatory restrictions on the use of municipal water.

It is almost 10 o'clock on a sunny night here in the tundra. Polar bears lumber through the rocky, treeless countryside. Huge chunks of white ice float just offshore in Hudson Bay. And at the mouth of the Churchill River, the roundup is on. Like aquatic cowboys, Eskimos stand at the bows of speeding motorboats, swinging lassos and shouting, ''Go! Go! Go!'' Suddenly, a young whale flashes past the side of a boat, rising partly out of the water to breathe. An Eskimo leaps onto it, throwing his rope around its head. The whale darts off, rider and all. Two Eskimos - then six - leap into the river after them. In the end, two dozen men will help handle the whale - almost 10 feet long, almost 1,000 pounds - one of five captured here this week as two aquariums in New York and Connecticut held their first whale expedition in eight years.

''The city came out smelling like a rose.'' - Mayor Tom Bradley of Los Angeles, describing San Francisco. (10:3.)

As the Democrats left San Francisco in a feisty and upbeat mood today, Walter F. Mondale opened his national campaign by challenging President Reagan to a series of six debates this fall on topics ranging from arms control to the environment. In a talk to the Democratic National Committee here this morning, Mr. Mondale said the televised confrontations could produce ''a great debate about all the deepest questions that bear on our future in a way that Americans will listen and decide.'' The Democratic nominee's challenge, if accepted, would result in the most debates ever held between Presidential candidates. Too Early, White House Says The White House spokesman, Larry Speakes, said that while Mr. Reagan was ''committed to the principle of debate,'' it was too early in the campaign ''to start a debate on debates.'' Mr. Speakes instead made a point of Mr. Mondale's assertion last night that taxes would have to be raised to reduce the budget deficit. ''This Administration,'' he said, ''has been talking and working for three years to ease the burden of taxation on all Americans and hold the growth of the Federal budget to responsible levels.'' (Page 12.)

Pharmacists across the country have begun using computers to avoid dangerous interactions among the prescription drugs patients take, the foods they eat, their allergies and the over-the-counter medicines they use. The Boston Collaborative Drug Surveillance Program at Boston University, a clearinghouse for information on the side effects of drugs, estimates that $4.5 billion in hospital bills and over 100 deaths result from such interactions each year. ''If there's a such thing as a wave of the future, this is it,'' said Dr. Edward G. Feldmann, vice president for scientific affairs of the American Pharmaceutical Association, the national professional society for pharmacists in Washington. ''Nearly every store will have some sort of system. It's a sound economic investment for the stores, and it's a major advance in the health care of patients.''

Today, Gary Hart became a collector's item, Mario Cuomo was a name that everybody wanted to learn to pronounce and Walter F. Mondale went fishing. As the Democratic National Convention ended, the city was awash in campaign detritus, heaps of suitcases, exuberant Democrats and memorabilia collectors. Sally Bowers, an 86-year-old widow, walked from her home to Moscone Center, where she wandered around looking at the remnants of the rostrum she had watched on television. ''To think all these governors and Jane Pauley were right here,'' she sighed. ''They were so inspirational, every one of them. Especially the Governor of New York, Kimona. Is that his name?''

The Environmental Protection Agency will soon propose new rules to reduce the lead content of gasoline by more than 90 percent in the next four years and to ban lead in gasoline entirely by 1995, agency officials said today. The announcement is likely before the end of this month, the officials said. They said the decision to issue the new rules was based on recent findings that lead is a more serious threat to the health of the public, particularly children, than previously believed. It was also based, they said, on findings that current rules would not reduce the lead content of gasoline as soon as had been hoped because many motorists are illegally putting leaded gasoline in cars that are supposed to use only unleaded fuel. More engine power can be obtained with leaded gasoline, which has a higher octane rating than unleaded fuel.

A group that describes itself as an alternative to Mexico's mainstream leftist parties has won a place on the ballot in next year's congressional elections. The group is the Mexican Workers' Party, and for its leader the recent decision by the Federal Election Committee to allow the group to run a slate of candidates marked the end of a 13- year struggle for recognition. ''We are offering an alternative to totalitarianism and an alternative to socialism,'' said the party leader, Heberto Castillo. ''We are the new left of Mexico.''