The Justice Department yesterday sued the Suffolk County, N.Y., police department, the 10th largest in the country, on charges of discriminating against blacks, women and Hispanics in hiring and promotion policies.

The lawsuit, filed by Assistant Attorney General William Bradford Reynolds in U.S. District Court in Brooklyn, said that the Suffolk County police force has violated the 1964 Civil Rights Act as well as various federal revenue-sharing and law enforcement funding laws by refusing to "recruit, hire, assign and promote" blacks, Hispanics and women on an equal basis with white men.

The department also is charged with using tests and other selection standards, including some that have no bearing on job performance, that have a discriminatory effect on these groups.

The Suffolk police force, in Long Island's easternmost county, has 2,580 officers and 890 civilian employes. Of the police officers, 25 (or 0.9 percent) are women and 59 (or 2.3 percent) are black or Hispanic.

Women and minorities are concentrated in the lower-level civilian jobs. Of the full-time civilian workers, 66 percent are women, 9 percent are black and 7 percent are Hispanic.

The Justice Department notes in the suit that the police department has not attempted to correct the problem. It said that since 1972 the department has hired 955 officers, including five blacks, 16 Hispanics and 27 women. There are no blacks or Hispanics above the rank of sergeant and no women above the rank of lieutenant, the department charged.