What was going on when I was born?

Inside Jorge Diaz Serrano's home in a fashionable Mexico City neighborhood, the trappings are of comfort and success; outside, they are of an armed camp. Mr. Diaz Serrano, the head of Mexico's national oil company under former President Jose Lopez Portillo, has become the first ''big fish'' of the new Government's effort to show it is committed to restraining corruption in high places. While other cases have been brought since Miguel de la Madrid Hurtado became President last December, none has matched the impact of linking the former director of Petroleos Mexicanos with a fraud of $34 million involving the purchase of two tankers. Followed by a Helicopter The Government is serious about not letting this one get away. Gun-toting men dart about on his street, and each time Mr. Diaz Serrano travels these days, according to his lawyer, he is followed by an entourage of six unmarked cars, a pickup truck equipped for off-the-road travel, two motorcycles and occasionally a helicopter.

The summer season, the hectic season, is under way at Pennsylvania Station in Manhattan. Seven days a week more than half a million people pass through the railroad station, one of the nation's busiest. Many are commuters traveling to and from homes as far away as Pennsylvania. Thousands more are vacationers, loaded down with luggage, coolers and tennis rackets. And travelers are not the only people there, of course. It's a city of its own. People work, eat, shop and even live at the station. Some people play the horses at the Offtrack Betting parlor. Others stop in to get out of the hot sun. Some nights businessmen are stranded after missing their last train. For Debbi Hoeler, an information clerk, summer in Penn Station means answering hundreds of questions a day, many from abusive customers. For Brad Rubin, a baker at a bagel store in the station, it means a full shift working near a 500-degree oven on an already hot day. For Michael P. Harmon, a police officer, it means controlling the derelicts and homeless people who wander the terminal at night.

It was 50 years ago that Congress erected barriers between commercial banks and other types of financial institutions to protect the banks from the kind of excessive risktaking that led to bank failures during the Depression. In recent years, however, a kind of de facto deregulation has been under way as aggressive bank managers have tried to expand into new areas. Congress is beginning to consider proposals for overhauling banking regulations, but there is still disagreement over what is appropriate. Treasury Secretary Donald T. Regan will testify Monday on behalf of an Administration bill to speed the pace of deregulation, by allowing banks to expand into real estate, insurance and some securities activities. Paul A. Volcker, chairman of the Federal Reserve Board, has in principle endorsed the Administration's proposal. But as a first step he has also urged that Congress impose a temporary freeze on crossindustry acquisitions, to give legislators more time to establish policy.

Senior Administration officials said today that they hoped to work out with President Amin Gemayel of Lebanon this week a new formula toward ending the impasse with Syria over the withdrawal of foreign troops from Lebanon. But Lebanese and United States officials offered differing evaluations of the likelihood of any early movement toward a solution of the problem. Foreign Minister Elie Salem of Lebanon, who is in Washington in advance of Mr. Gemayel's arrival on Wednesday, expressed optimism today that Syria's adamant refusal so far to negotiate a withdrawal was only a temporary, tactical move. No Fear of Partition Mr. Salem also said he had no fear that either Israel or Syria had plans for any permanent partition of his country. ''I am confident that we will break the stalemate and then we will have progress and phases that will show encouragement and then we can regain a momentum that I think we have lost in the past two months,'' Mr. Salem said.

The Presidents of four Latin American countries tonight expressed ''profound concern for the rapid deterioration'' of the situation in Central America. They called for the removal of foreign military bases and advisers, a freeze on arms shipments and establishment of international border patrols as key steps to achieving peace in the region. The four leaders, Miguel de la Madrid Hurtado of Mexico, Luis Herrera Campins of Venezuela, Belisario Betancur of Colombia and Ricardo de la Espriella of Panama, made their appeal after five hours of meetings at this resort island. It was part of a broader program that built upon six meetings held by their foreign ministers earlier this year.

Tom Watson broke a three-way tie with a birdie 3 on the 16th hole today to win his fifth British Open Championship by one stroke. The finish of this 112th Open Championship was one of the tightest in modern times, with eight players sharing the lead at one juncture or another. Five were tied for first place at 4:40 P.M., when Watson, in the last pairing of the day, was on the 12th hole. Sixty-five minutes later, when the jam was reduced to three, Watson moved out in front.

President Reagan is giving ''serious consideration'' to naming former Secretary of State Henry A. Kissinger chairman of a bipartisan commission aimed at seeking support for the Administration's policies in Central America, a senior Administration official said today. The official said President Reagan planned to call for creation of such a commission in a speech Monday to the International Longshoremen's Association in Fort Lauderdale, Fla. As he was returning to the White House from a weekend at Camp David, President Reagan was asked tonight whom he would name to the panel. He replied, ''Wait.''

The gap between the average incomes of whites and blacks is as wide today as it was in 1960, primarily because the proportion of black families headed by women rose from one-fifth to nearly one-half and the proportion of black men with jobs dropped sharply in that period. Those were the principal findings of the first nonpartisan, comprehensive report on the status of blacks since the 1980 census and subsequent data were published. The study was conducted by the Center for the Study of Social Policy, a private research group headed by a Nixon Administration official. The study shows that black and white families were, on the whole, better off than in 1960, largely because both parents work in so many more families nowadays. In fact, black families in which the husband and wife work increased their earnings at a faster rate than did white families.

A picture caption in Weekend on Friday with a review of the Riverside Shakespeare Company's ''Merry Wives of Windsor'' misidentified the actress. She is Sonja Lanzener.

As oil ministers arrived here today for a semiannual meeting of the Organization of Petroleum Exporting Countries, there appeared to be little chance that disputes within the group would erode its basic production and pricing policies. The meeting will be held Monday and Tuesday. The only official business today was a midday gathering of the four-member Market Monitoring Committee, which spent just over an hour preparing its report to the delegations from the 13 OPEC members. No statement was issued, but the brevity of the meeting reinforced the feeling that the ministerial gathering was likely to be uneventful.

''Walter, will you come down already,'' Anna Heinemann said. ''Mr. Cook is here.'' ''I'm moving as fast as I can,'' Mr. Heinemann said. William Cook plopped down into a chair in the dining room of the Heinemann home in Maywood, N.J., last week and opened a folder. He is a representative of Investors Diversified Services Inc., the big financial products company, and had stopped by to review Anna and Walter Heinemann's account. Like a dentist, he tries to see his clients every six months. Mr. Heinemann, a retired tailor, was not in tip-top medical shape. Mr. Cook wondered if the Heinemanns might want to switch one account into Mrs. Heinemann's name.

International The removal of foreign military bases and advisers from Central America was called for by the Presidents of four Latin American countries, who, at a meeting in Mexico, expressed ''profound concern for the rapid deterioration'' of the situation in Central America. They also called for a freeze on arms shipments and the establishment of international border patrols as key steps towards peace in the region. The Presidents of Mexico, Venezuela, Colombia and Panama attended the meeting in Cancun. (Page A1, Column 6.) Henry A. Kissinger might head a proposed bipartisan commission aimed at seeking broad political support for the Administration's policies in Central America. A senior Administration official said President Reagan is giving ''serious consideration'' to appointing the former Secretary of State as the commission's chairman. He said Mr. Reagan planned to call for the creation of the commission in a speech today at a meeting of the International Longshoremen's Association in Fort Lauderdale, Fla. (A1:5.)