The Justice Department and the NAACP have sharply criticized a desegregation plan drawn up by officials in Yonkers, N.Y., to settle a suit in which the city was found guilty of systematic bias in its housing and schools.

A U.S. District Court judge in New York began a separate trial yesterday on the city's proposed remedies, which NAACP attorney Michael Sussman dismissed as "a joke" and "a do-nothing plan."

Judge Leonard B. Sand ruled in November that Yonkers officials have maintained a segregated school system for three decades, in part by refusing to build low-income housing on the exclusive east side of town. All the public housing and deteriorating black schools are west of the Saw Mill River Parkway, which acts as a racial dividing line in the Westchester County suburb.

Yonkers officials have proposed two locations for new low-income housing, but the Justice Department said in court papers that the sites -- one of which is a few hundred feet from the parkway -- are isolated and have been rejected by federal housing officials.

The city's plan also relies on developers to build middle-class housing and reserve 20 percent of the units for poor families. Justice officials, who sued Yonkers with the NAACP, said the city "failed to demonstrate that its proposal is feasible" and that the plan is "nearly totally dependent on . . . private developers."

Yonkers corporation counsel Arthur J. Doran said the city prefers to rely on developers "so we would not have a heavy concentration of all low-income minorities on those two sites." He said federal housing officials rejected the sites because of "pressure from the NAACP," which he called "unreasonable."

The school board, meanwhile, has submitted a plan that "does not promise realistically to effectively desegregate the Yonkers schools," according to the Justice brief. Department officials said the plan "unnecessarily burdens minority students" because nearly all the busing required would send black students into white districts.

The plan relies mainly on school closings and voluntary transfers to new magnet schools. Sussman said the plan would leave three elementary schools more than 80 percent black.

Schools spokesman Debra Heller said the magnet plan is "very strong and very attractive" and offers the best long-term hope for integration. But Sussman said the school board plans to upgrade programs for the largely white schools, "the very schools from which they expect white middle-class parents to transfer their kids."