What was going on when I was born?

Construction of new housing rose by 6.4 percent last month, rebounding from a two-month decline and putting such building activity 29 percent above the period a year ago, the Commerce Department said today. Work was started on new housing at an annual rate of 1.76 million units in November, compared with a rate of 1.65 million units in October, the department said. The new figures included gains for single-family homes and buildings with two to four units, and a decline for housing with five or more units.

Transcript of news session, page A22. WASHINGTON, Dec. 20 - President Reagan said today that he envisioned the role of United States marines in Lebanon as moving in behind the Lebanese Army to provide security as it sought to expand its control throughout the country. At a news conference, Mr. Reagan said the objective of the American troops, joined by other participants in the multinational force, was to ''try to achieve some stability and maintain order'' as the Lebanese Army expanded its role. After the news session, an Administration official said the President was not offering a broader definition of the role of American troops in Lebanon. He said Mr. Reagan was describing the current situation of the multinational force stationed in Beirut while the Lebanese Army seeks to move into the Shuf Mountains to the southeast.

Every day for two years, a contingent of New Jersey state troopers has come to a makeshift command post in the basement of Town Hall here, waiting for the tip that will crack their biggest investigation in a half-century. Eight-tenths of a mile from the tiny nerve center is the spot where a highly decorated state trooper, Philip Lamonaco, then 32 years old, was shot eight times and killed on Dec. 21, 1981, during an apparently routine traffic stop on a stretch of Interstate 80 that cuts through desolate hills and farmland near the Pennsylvania border. In the two years since then, the state police have implicated the remnants of a New England radical group - the Sam Melville/Jonathan Jackson Unit - in the murder. Four men and two women are being sought. The hunt has stretched nationwide and into Canada. Police officials say the hunt has cost $1 million.

Mark Helprin is the author of ''Winter's Tale'' (Harcourt Brace Jovanovich). ABOUT 30 years ago, when I was a small boy, I figured out that I was unable to appreciate material objects in a normal fashion. My heart did not leap at the sight of a wrapped present, and soon after opening it I wanted neither it nor something else to want after it, because it was clear to me that things in themselves, when they are not symbols, do not have the power to make anyone happy in a decent way that will last. In the strange position of a child who wanted no presents, I wondered what the approaching Christmas would be like, especially since I realized that because I was Jewish the religious option (certainly the finest and in America the most neglected part of this holiday) was simply not open to me. It seemed as if I would pass through that Christmas as if through a vacuum, and I thought there would be nothing for me. But I was wrong.

Texts of House subcommittee's report and of dissent, page A18. WASHINGTON, Dec. 20 - President Reagan said tonight that he did not think Gen. Paul X. Kelley, Commandant of the Marine Corps, ''was attempting to cover up for anyone'' when he testified before Congress about the destruction of the Marine headquarters in Beirut by a terrorist truck bomb on Oct. 23. A report issued Monday by a House subcommittee was highly critical of the Marines and said the testimony given by General Kelley and other Marine Corps and Administration officials ''was found to be often inaccurate, erroneous and misleading.'' It added, ''While not intentionally misleading, this testimony hindered the subcommittee and delayed its inquiry.''

Roger B. Smith, chairman of the General Motors Corporation, said today that the company was willing to sign a consent order promising not to violate antitrust laws in its planned venture with the Toyota Motor Corporation. The order was requested by the staff of the Federal Trade Commission before approval is given for the auto maker's link with Toyota in a California auto-making project. In Washington, a commission official said of the G.M.-Toyota talks on the consent order: ''They really have reached agreement and they're just polishing it up.'' A vote is expected Thursday, and commission aides said the F.T.C. would approve. Commission sources said it appeared that James C. Miller 3d, the F.T.C. chairman, and two members, George W. Douglas and Terry Calvani, would vote in favor, with Michael Pertschuk voting against. Patricia P. Bailey has apparently still not made up her mind.

Because of an editing error, an article in some copies of Business Day on Friday about the GTE Corporation's Sprint telephone service misstated the charge for business customers. They pay a minimum of $25 a month.

By day, John Hadity is a programmer in an advertising agency in Manhattan. By nights, this Christmas season, he is on the fifth floor of Bloomingdale's, hawking a $10 toothbrush that plays an electronic rendition of ''Silent Night.'' Even though the 22-year-old Mr. Hadity works at Bloomingdale's only 10 hours a week, his earnings can be pretty good. One recent evening he sold 18 toothbrushes in an hour and a half, making a $2 commission on each one.

A Palestinian leader said here today that he and other prominent Palestinians were trying to organize an emergency meeting of all factions of the Palestine Liberation Organization to prevent the 19-year-old group from disintegrating. The statement was made in an interview by Khaled Fahum, chairman of the Palestine National Council, the organization's parliament, which is based here. He said that unless the factions reconciled their differences, ''there will be two P.L.O.'s, and two P.L.O.'s mean there will be no P.L.O.'' ''Two P.L.O.'s mean the end,'' he said. No Formal Split in the P.L.O He spoke as Yasir Arafat, the chairman of the P.L.O. and head of Al Fatah, the largest faction, was being evacuated from the Lebanese city of Tripoli with 4,000 loyalists. The Arafat force, Mr. Fahum noted, has lost its military battle against Syrian- supported Palestinian rebels, but the organization has not been formally split.

In an unusual intervention, the Commerce Department has asked the Export- Import Bank to turn down a loan of more than $100 million that the bank is considering to finance sales of American-made equipment for a South Korean steel works. In a letter to the bank, Lionel H. Olmer, the Under Secretary, said he was acting because of ''serious oversupply worldwide'' in steel and because ''increased Korean steel exports would be aimed primarily at the U.S.,'' increasing demands for trade protection by workers and industry in the United States. A similar appeal has been made by organized labor.

WEDNESDAY, DECEMBER 21, 1983 International G.M. is willing to sign an antitrust consent order to secure approval from the Federal Trade Commission of its joint venture with Toyota, the company said. Toyota officials also said an agreement is near. The vote by the commission is expected tomorrow, and commission aides said approval would be given. (Page D1.) A Korean steel plant should be blocked from receiving a $100 million Export-Import Bank loan for equipment, the Commerce Department says, because ''increased Korean exports would be aimed primarily at the U.S.'' (D1.)

After three years of hard times, the credit rating of American farmers has been improving in recent months as the recession has receded, and the number of farm foreclosures and bankruptcies seems to be declining, according to bankers and Agriculture Department officials. Commercial bankers throughout the major agricultural regions and those who run Government lending programs say adequate loan money will be available to farmers in 1984 and that most of their farmer borrowers will be able to get it. But these officials also warned that hundreds of thousands of farmers still carry dangerously large debts at high rates of interest as a result of years of overambitious borrowing and easy credit offered by the Government and private lenders. Loan officers said that they had tightened their credit practices this year but that serious problems lingered. At the Agriculture Department, Frank W. Naylor Jr., the Under Secretary for small community and rural development, who is the official who charts all types of farm loans, asserted: ''The re ' ll be no shortage of credit next year for most farmers. But all lenders to farmers are going to be looking more closely at their farm loans and making sure crop and livestock producers have sound operating plans for 1984.''