December 22, 1986

The Internal Revenue Service, contending that at least 1.1 million Americans have failed to provide their financial institutions with accurate Social Security numbers, has begun a tough enforcement program to combat the problem. The I.R.S. believes that problem of inaccurate or missing numbers reflects, at least partly, attempts by individuals to underreport dividend and interest income. Some tax experts say that 1.1 million is a conservative figure and that the real number is many times that. Whatever the magnitude of the problem, the I.R.S. is fighting back. According to top tax accountants, the agency recently sent letters to 23,000 financial institutions - banks, savings and loan associations, credit unions and brokerages - informing them that in at least 50 instances each, customers had failed to provide the financial institution with a Social Security number or had provided an incorrect one.

John Z. DeLorean, the embattled automobile entrepreneur, said this weekend that he had raised $20 million to build a new car, a $100,000 sports car to be designed by a West German designer. The announcement follows Mr. DeLorean's acquittal last week of charges that he had embezzled $8.5 million from investors in his previous enterprise. In that venture, Mr. DeLorean made a stainless-steel sports car with gull-wing doors, the DMC-12, at a plant in Northern Ireland in 1981 and 1982.

Six years after Jean S. Harris was convicted of killing Dr. Herman Tarnower, the author of the best-selling ''Scarsdale Diet,'' the case is once again arousing debate. The issue this time is punishment. Mrs. Harris, the 64-year-old former headmistress of the Madeira School in Virginia and now New York State prisoner 81-G-98, has written a letter to Governor Cuomo requesting clemency, which would make her eligible for immediate parole. Convicted of second-degree murder in the shooting, she is serving 15 years to life at the Bedford Hills state prison in Westchester County. The Governor has said he will give Mrs. Harris's request his ''very, very best judgment'' when it reaches his desk, but has declined to comment further. His office has declined to say when he might announce decisions about clemency. It has been a tradition in the state for the decisions to be made in the December holiday period.

For the first time in 15 years, the Kansas City Chiefs will be spending the holiday season with more than just family and friends. A 24-19 victory over the Pittsburgh Steelers yesterday, the final Sunday of the National Football League season, put them into the American Football Conference wild-card game next Sunday. With the exception of New Orleans, which has never been in the playoffs in its 20 seasons, the Chiefs are the only N.F.L. team that has not participated in postseason play since 1971. The Chiefs' opponent, however, will not be determined until tonight, when the New England Patriots play the Miami Dolphins in the final game of the regular season and the Dolphins' last game in the Orange Bowl.

It is not even a subway - only 150 yards or so are enclosed in a tunnel. But that did not prevent the Staten Island Rapid Transit system from doing what subways in New York seem destined to do: fall apart. The bridge carrying the railroad's two tracks over Bay Street in Clifton, having moved six and a half inches while no one was looking, is now braced with timber, awaiting permanent repairs. Floods at Richmond Valley sometimes cover the third rail, knocking out service.