December 17, 1983

The cost of a ride on the city's subways and buses was raised yesterday to 90 cents, a 15-cent increase. The new fare, to take effect next month, is the first increase in two and a half years. The increase was approved by the board of the Metropolitan Transportation Authority, which also voted higher fares for its rail commuters and raised some bridge and tunnel tolls. Fares will rise an average of 20 percent on the Metro-North Commuter Railroad and the Long Island Rail Road. Bridge and Tunnel Fares Tolls at four bridges and two tunnels operated by the Triborough Bridge and Tunnel Authority will go to $1.50, from $1.25.

A steady 10-year decline in New York City's welfare rolls has ended, and in the last year the number of people on welfare has risen to more than 900,000. A substantial part of the growth in welfare rolls, city officials said, can be traced to a growing number of single people who cannot find employment and must rely on public assistance to live. ''Welfare rolls go up when there is unemployment and broken homes,'' Mayor Koch said. ''Regrettably, both factors exist today as causes for the increase.''

President Raul Alfonsin said today that he had set up a commission to investigate the disappearances of more than 6,000 Argentines during the military Government of the last several years. He said evidence turned up by the panel would be given to the courts for prosecution. It was the latest in a series of forceful measures Mr. Alfonsin has taken in his first week in office to rectify the abuses of nearly eight years of military rule. The nature of the actions and the speed with which the new President has ordered them have surprised many Argentines.

Billy Martin's third term as manager of the Yankees ended with his dismissal yesterday, almost a year after it began. And Yogi Berra's second term began, 19 years after his first one ended. The change was the 11th in 11 years made by George Steinbrenner, the principal owner of the team, who said: ''I don't like to talk about firing managers. I'm shifting people in everyone's interest: Billy's, Yogi's, mine.''

The Producer Price Index, the leading gauge of industrial price changes, declined two- tenths of 1 percent last month, the first drop since spring, the Government reported today. The Labor Department, which compiles the index, attributed the November decline to 1 percent drops in both food and energy prices. The index is for finished goods, products on which manufacturing has been completed. It has risen less than 1 percent for the last 12 months, its smallest increase since 1964 and another reflection of the overall economy's unexpectedly good health.