What was going on when I was born?

The Army's new Chief of Staff, Gen. John A. Wickham Jr., asserted today that poor performance of arms and equipment in his service was largely due to deficiencies in quality control in American industry. For instance, he said, all five failures in 16 flight tests of Pershing 2 missiles were caused by mistakes made by the contractor. The Martin Marietta Corporation of Bethesda, Md., is the company primarily responsible for making the medium-range missile, which is scheduled for deployment in West Germany in December. A spokesman for the missile producer, reached by telephone in Orlando, Fla., declined to comment.

A 13,000- square-foot ceiling crashed down at the PATH railroad line's Journal Square center here today, killing two people and injuring eight others. Even as emergency crews cut through the tangle of debris in a search for victims, officials of the Port Authority of New York and New Jersey announced that a ''sag'' had been found in the ceiling in April and that the ceiling collapsed while three workmen were trying to make minor repairs. The officials said there had been no reason to believe the structure was ''in imminent danger of collapse.'' The ceiling - 150 by 90 feet and estimated to weigh 50 tons - gave way at about 9 A.M., shortly after the height of the morning rush hour. Service Halted Six Hours Some 60,000 bus and rail commuters a day go through the center, 27,000 of them on the PATH line. The accident shut down all PATH service between Newark and Manhattan for more than six hours.

The White House has told the Treasury not to support a new effort in the House of Representatives to tax such employee fringe benefits as free airline tickets or use of company cars, according to a top Treasury official. Taxing such benefits may be good tax policy, he said, but it is bad pre-election year politics. ''We're going to shuffle and waffle on this one,'' the Treasury official said in commenting on the decision against a new House Ways and Means Committee bill that would, for the first time, make some fringe benefits taxable as income. ''The people who get these fringe benefits,'' he said, passing on the White House reasoning, ''are our constituents, the middle class.''

International In Guatemala, a military coup brought down the Government of Brig. Gen. Efrain Rios Montt. Brig. Gen. Oscar Humberto Mejia Victores, the Defense Minister, was sworn to succeed General Rios Montt, whose fate was not known. The new leader pledged to legalize political parties and hold elections for a constituent assembly in July that would lead eventually to presidential balloting. It was the country's second coup in 17 months. (Page A1, Column 6.) The Reagan Administration reacted with caution to the coup in Guatemala. Administration officials said it was difficult to predict how the change would affect United States- Guatemala relations or Guatemala's role in Central America. (A11:1.)

Because of an editing error, an article in Business Day on Saturday regarding withholding taxes and foreign trade incorrectly described imports from the Caribbean that can enter the United States duty free. Textiles, apparel, leather goods and watches from the area cannot enter duty free.

Stock prices plunged yesterday in slightly brisker trading after most major banks increased their prime lending rates. The Dow Jones industrial average, which was in the minus column throughout the session, dropped 20.23 points, to 1,163.06, its lowest closing level since April 13, when it finished at 1,156.64. In the past six trading sessions, the key average has fallen 36 points, mainly because interest rates have been increasing on the credit markets. The selloff was across-the-board, with stocks that fell in price on the New York Stock Exchange outscoring those that advanced by almost a 4-to-1 ratio. Turnover on the Big Board expanded to 71.5 million shares, from 67.9 million shares on Friday.

The energy crisis may be over, but don't tell Mother. Mother Earth News, a magazine published six times a year in this small town at the foot of the Smoky Mountains, has been preaching self- reliance - in fuel, food and other necessities - since it was founded in 1970, and that message is still the foundation of the company. Mother Earth News is unrelated to the Whole Earth Catalog, which is based in California. In the past three years, however, following the acquisition of Mother Earth News Inc. by three of its employees, the magazine's revenues and circulation have doubled, to $20 million and 900,000 copies a year. Now the owners are examining money- making ventures that could more than double sales again by 1990, according to Robert Lieb, the publisher.

Group health insurers in New York State will be required to pay for at least 60 days of outpatient treatment a year for alcoholism under a bill signed today by Governor Cuomo. Currently major insurers provide limited benefits for alcoholism treatment under their basic plans, usually limited to treatment in hospitals for detoxification. Mr. Cuomo said the new legislation will encourage more people to enter treatment in the early stages of the problem, ultimately reducing the cost for care. ''Damage done to family relationships and personal potential cannot be measured in monetary terms,'' Mr. Cuomo said. ''Whether an alcoholic seeks treatment depends largely on whether he or she has adequate health insurance coverage.''

''For the four years of high school, the school locker is a home away from home.'' - Associate Justice Daniel J. O'Hern of the New Jersey Supreme Court. (A1:1.)

Marc Rich & Company A.G., the big commodity-trading concern under investigation for possible tax evasion, paid a fine of $1.25 million yesterday. The fine was part of an agreement reached Friday with Government investigators to resolve a year-long fight over documents subpoenaed by a Federal grand jury. Marc Rich also dropped a lawsuit it had filed to quash a contempt charge against it.

Jury selection was completed today and opening statements begun in the Brink's murder and robbery trial, but the three defendants left the courtroom in a dispute with the judge. The three, who only this morning had ended a nearly two-week boycott of the court proceedings during the four-week jury selection process, chanted slogans and raised clenched fists as guards escorted them out shortly before 3 P.M. They announced their departure after the presiding judge, David S. Ritter of Orange County Court, had refused to allow one defendant, Kuwasi Balagoon, to continue reading a written statement. The statement, which he had been reading for a half-hour at that point, focused largely on his radical background and political views in support of a separate black nation. Another defendant, David J. Gilbert, shouted as he left under guard, ''All the oppressors will fail!'' Similarly the third defendant, Judith A. Clark, left shouting, ''Death to U.S. imperialism!'' Courtroom Is Cleared A dozen or so supporters in the tiny courtroom stood and echoed such slogans as ''Free the land!'' until the judge ordered a recess and the heavily guarded courtroom was cleared.

An article on ''Chad at a Glance'' yesterday misidentified the former president who now leads a rebellion in the country. He is Goukouni Oueddei.