What was going on when I was born?

International Early returns in El Salvador indicated that the moderate Christian Democrats had won more votes than any of the five other parties in Sunday's elections, but the victors' final total would not give them a majority in the new constituent assembly. The extreme right-wing Nationalist Republican Alliance led by Roberto d'Aubuisson, a controversial former army major, was in what the United States Ambassador called a ''strong second position.'' (Page A1, Column 6.) The Administration was jubilant over the apparent victory by Salvadoran moderates. Secretary of State Alexander M. Haig Jr. called the voting ''a victory we have all won.'' (A1:5.)

Five men described as members of the Bonanno crime family were indicted by a Federal grand jury in Manhattan yesterday. The charges against them included conspiracy to murder rival gang members and the attempted robbery of a Manhattan town house owned by the sister of the late Shah of Iran. Six other men said to be members of the Bonanno organization were indicted on similar Federal racketeering charges last November. A Federal Bureau of Investigation official, Richard T. Bretzing, said the 11 indictments had ''severely wounded'' the Bonanno group, which law-enforcement agencies list as one the five major organized crime factions in the New York metropolitan area.

Rescue workers early today abandoned a day-long effort to tunnel to a 48-year-old Scoutmaster wedged inside an old cave here and began digging away the entire hillside housing the cave. Col. Clinton L. Pagano, Superintendent of State Police and one of the leaders of the rescue operation, said destruction of the hillside posed the risk of killing the trapped man, Donald Weltner, if, in fact, he was alive. But Colonel Pagano said the ''quarrying operation,'' as he described it, offered the only possibility of freeing Mr. Weltner. ''We have nothing left, no further options to pursue,'' Colonel Pagano said at 12:05 A.M. today. ''It eliminates the possibility of getting him out of there with a chance of resuscitation.''

The Price of Health Examining the Medical System Third of five articles. By LAWRENCE K. ALTMAN At a time when the cost of medical care is soaring and doctors are being urged to practice more cost-effective medicine, many people are asking these basic questions: How good is American medical care in relation to its cost and what would have to be sacrificed in terms of quality to reduce that cost? The technological sophistication of American medicine is regarded as unsurpassed. The expertise of this nation's doctors in applying it has helped extend the lives of millions of people and has improved the quality of life for millions more. And the gains have occurred concurrently with a huge American investment in health. From 1940 to 1980, the share of the gross national product devoted to health care rose to 9.4 percent from 4 percent.

THEY are all world-famous: 100 young concert pianists, Olympic swimmers, tennis players and research mathematicians who reached the top of their fields between the ages of 17 and 35. But their names are the secret of a research team at the University of Chicago that promised anonymity in order to investigate how these exceptionally talented people got where they are. After completing their analysis of the life histories of these outstanding people, the investigators, headed by Prof. Benjamin S. Bloom, one of the nation's foremost educational researchers, have identified several conditions that stand apart from native gifts and, in nearly every case, appear crucial in producing excellence. ''The old saw that 'genius will out' in spite of circumstances is not supported by our study,'' Professor Bloom said. As the data emerge from the study, they seem to show that most human beings are born with enormous potential - in one area or another - and also demonstrate the extraordinary power of parents.

SMALL buff-colored lumps are mottling the bark of tree trunks and limbs all over the Northeast again this spring, raising the likelihood of another massive infestation of gypsy moths. As the days grow warmer, the lumps will split open, freeing untold billions of caterpillars that will start to do the thing they do best: eat leaves. The devastation wrought by these caterpillars has led to intensive efforts to better understand them and some promising approaches for controlling them, but their spread throughout most of the country is expected to continue for some time. Since its accidental introduction in New England more than 100 years ago, the gypsy moth has slowly spread west and south. But dramatic population explosions caused five million acres of trees to be stripped of their leaves in 1980 and some 13 million acres were defoliated in 1981, levels far surpassing those of previous years. Last year the insect caused visible defoliation of trees in 11 Eastern states, and smaller infestations have recently been found in 19 other states, including California, Washington and Oregon.

Last November, as the second flight of the space shuttle Columbia was ending, some of the space agency's top engineers looked back at the string of equipment failures that had afflicted the first two flights. Having just been forced to cut the second mission short because of one such failure, they conceded that they had created a machine so complex that they had not yet mastered it. So until they developed more confidence, they said, they would have to treat the space shuttle cautiously and gingerly. Last night, as Columbia was preparing to land after completing all the major tasks of its third and next-to-last test flight, Neil Hutchinson, one of the three flight directors who had taken eighthour turns at running the mission, offered this assessment of how far things had come during the last week: ''You have to believe that we're a gigantic step closer to having a vehicle that doesn't require as much babysitting.'' That, said Mr. Hutchinson, ''is what the operations thing is all about.'' None of his assessment was negated by today's one-day postponement of the shuttle's landing, made necessary by high winds at the White Sands, N.M., landing site. In fact, the postponement and the subsequent decision to consider landing at Kennedy Space Center in Florida were taken as evidence of the flexibility with which the shuttle may be able to operate.

An article on Detroit yesterday incorrectly identified the city in which Rosa Parks inspired a civil rights struggle. The city is Montgomery, Ala.

The Chase Manhattan Bank is planning to establish a new subsidiary for its investment banking activities that would be comparable in size to Bache Halsey Stuart Shields & Company, one of the nation's 10 largest securities concerns, the bank said yesterday. Under the plan, which is to be formally announced today, Chase will merge all its securities trading and capital market activities, domestic and international, into a single subsidiary of the bank. The company will not enable Chase to enter new fields at present because it, like the bank, will be subject to the Glass-Steagall Act that limits the types of investment banking activities in which commercial banks may engage; most importantly, underwriting corporate securities is prohibited.

The directors of Marshall Field & Company yesterday sought another increase from Batus Inc. in the value of its proposal to acquire the Chicago retailer, financial sources reported. The move was seen as an effort to keep Field's shareholders from withdrawing stock already tendered or from waiting to tender their shares in the belief that a better offer from another company might appear. Field directors, meeting yesterday into the evening in Chicago, reportedly approved a proposal that Batus offer $30 in cash for all of the big retailer's outstanding common stock. A Field spokesman, who asked not to be identified, said that the company would make no announcement until today concerning the decisions taken at the meeting.

President Reagan offered a five-step plan to help the housing industry in a talk before the National Association of Realtors. Under his plan, pension fund investments in the credit markets would be increased and Federal regulations on home mortgages would be eased. (Page D1.) Sales of new single-family houses dropped 11.8 percent in February. (D18.) Contracting for new construction fell 16 percent, to $8.88 billion, in February. (D18.) Whether the Government can force two people who are married to sell their home to pay off taxes owned by one of them will be decided by the Supreme Court. (D6.)

The Supreme Court removed today any remaining doubt that New Jersey voters will elect their members of Congress this year according to disputed district lines adopted in January by the Democratic-controlled State Legislature. Without comment, the Court rejected an urgent request by the state's seven Republican Representatives to vacate a stay that Associate Justice William J. Brennan Jr. granted two weeks ago. Justice Brennan, acting then at the request of the state's Democratic leadership, issued a stay of a decision by a three-judge Federal court that declared the new district lines unconstitutional.