A bill to sharply limit the number of Japanese autos imported to the U.S. for the next three years is expected to be introduced today by a group of bi-partisan senators, sources said.

The legislation will be announced by Sen. John C. Danforth (R-Mo.), chairman of the Senate Finance International trade subcommittee. The bill, to restrict sales of Japanese imports here to 1.6 million units a year, would closely follow requests by the United Auto Workers Union and the Ford Motor Co. that quotas be based on what Detroit considers "normal" years of imported car sales -- 1975 and 1976. A total of 8.5 million foreign and domestic cars were sold in 1975 and 10 million in 1976.

Ford and the UAW had requested temporary relief because they said they needed the time to retool their plants to build their own small, fuel-efficient cars to compete with the Japanese. The industry is planning $80 billion in modernization through 1985.

The legislation would come at a time when the Europeans are considering limits on Japanese imports because they claim the Japanese are taking advantage of their depressed economies, and they need to protect their own auto industries.

The Japanese government, under pressure from U.S. officials, has asked its companies to be more prudent in their sales of cars abroad. But the Japanese automakers have contended that they are merely filling a need of American consumers that Detroit automakers were unable to fill and that they are considering locating plants here to put laid-off American automakers back to work. Imports aren't the cause of Detroit's problems, the Japanese contend. They blame the recession, high interest rates, high gasoline prices and inflation.

In addition to cries from the private sector for relief, former Transportation Secretary Neil Goldschmidt, a week before he left office, recommended mandatory import quotas. Last year of 2.6 million cars imported into the country, 2 million were from Japan, compared with 1.9 million foreign cars imported in 1977 of which 1.3 million were from Japan.

Late last year Sen. Donald Riegle (D-Mich.) and Sen. Carl Levin (D-Mich.) attempted to have passed a resolution giving the president authority to restrict imports. But that bill failed in the waning hours of the senate. At that time Danforth vowed that as chairman of the Senate Finance Committee international trade subcommittee he would hold hearings and soon submit legislation to help Detroit.

Several hearings were held last month at which Ford, Chrysler Corp. and General Motors representatives testified that they needed help from the government for their recovery from $4 billion in losses last year. Chrysler suggested that imports, which account for approximately 27 percent of the U.S. market, be restricted through a gentlemen's agreement with the Japanese to stop for two years sales of cars here that are built on overtime. That agreement would reduce imports by about 500,000 cars a year.