March 30, 1981

New York City announced yesterday a series of steps that it hoped would unsnarl weekday traffic in Manhattan's business districts. As part of the plan, greater traffic access will be provided in lower Central Park, and the distance between bus stops on Madison and other avenues will be increased. The plan, which will be introduced beginning today, follows Mayor Koch's decision two weeks ago to begin a ticket-writing blitz against double parking in midtown. Other parts of the program include the painting of ''antigridlock boxes'' at 10 clogged intersections and the creation of lanes exclusively for buses on a number of the avenues.

There was a scowl on Billy Cunningham's face with every Philadelphia mistake. There was a snap of the fingers when Kevin McHale blocked two straight shots by Julius Erving, and angry words when Maurice Cheeks lost the ball or Larry Bird stole it from him. Frustration ran high for Cunningham as the Boston Celtics defeated his Philadelphia 76ers, 98-94, today before a capacity crowd of 15,320 at Boston Garden. For three periods the Celtics dominated on defense. When the 76ers finally woke up with a 35-point fourth quarter, it was too late. .

Business bankruptcies are spreading through the nation's economy at a spectacular pace, largely because of last year's recession and current high interest rates. In the first 10 weeks of this year, business bankruptcy filings soared to 2,933, a gain of 63 percent from the comparable period last year and the highest number reported for the period since 1963. The gain early last year was already 53 percent above that for the similar period in 1979, according to data released last week by Dun & Bradstreet Inc. While the rash of business failures has swept across nearly the entire spectrum of business concerns - manufacturing, wholesaling and retail services have all experienced increases of more than 60 percent - a few areas were especially hard-hit. Problems in Housing and Autos ''Contractors are really taking a bath around the country,'' said Leonard Andrews, whose company publishes the National Bankruptcy Reporter, a legal newsletter. New housing construction plunged 25 percent in 1980, its worst performance since 1975, ruining many small contractors.

Indiana is a slight favorite over North Carolina to win the 43d annual National Collegiate Athletic Association basketball championship when the two teams meet tomorrow night in the Spectrum. However, no coach in college basketball or other person was willing to come out strongly in favor of the Hoosiers for what is expected to be one of the most physical and closely fought finals in many years. Meanwhile, Bobby Knight, Indiana's coach, spent much of the time at a news conference today explaining a shoving incident he was involved in with a Louisiana State basketball fan last night. The altercation occurred at the Cherry Hill Inn in New Jersey just a few hours after the Hoosiers had beaten L.S.U., 67-49, in the first semifinal game. Knight said the incident stemmed from an obscene remark made by the fan. No charges were filed.

''We must know that Solidarity is in the first place the working class itself.'' - Kazimierz Cypryniak, a Communist Party official from Szczecin. (A8:3.)