The Justice Department has eased legal standards for determining whether school systems can be declared desegregated and therefore be released from court-ordered busing and other antidiscrimination plans, according to court documents and department attorneys.

The standard, which has met mixed acceptance from U.S. judges, would allow school districts to be released from court orders when they have "fully and in good faith" taken the steps required by a desegregation plan, according to Deputy Attorney General Charles E. Cooper. Previously, the department, following the standard applied by other administrations, demanded tangible results.

School districts were required to "eliminate the vestiges of state-imposed segregation" or at least to achieve the results projected in a consent decree or court order. A district that met that standard was declared "unitary" by the courts and released from court supervision with the government's approval.

"We believe that . . . some short fall in terms of result . . . may not necessarily mean that the school district isn't unitary," said Cooper, adding that the failure to achieve the goals of a consent decree can result from factors over which a school district has no control, such as "demographics, the natural movement of Americans into and out of a school district."

To be released from court order, the Justice Department also requires that school officials show they had refrained from intentionally segregating the schools during the court-supervised period. This is unchanged from the older guidelines.

Lawyers for several school boards praised the department's "fully and in good faith" standard while lawyers for black schoolchildren criticized it.

"This makes a mockery out of Brown v. Board of Education and all the struggle that has gone into implementing it for the United States government to say that a school district can be relieved of its obligations without ever having desegregated the schools," said William Taylor, director of the Center for National Policy Review who has argued school desegregation cases for black plaintiffs.

But Robert C. Campbell, a lawyer for the Mobile, Ala., County Board of Education, praised the department's position.

"If we agree we'll do A,B,C and for some unknown reason A,B,C doesn't work out, like we have a disastrous flood or there's demographic movement and all the whites are clustered and the school system has nothing to do with it, that should end the case," he said.

The department is seeking a proper case to test the standard before the Supreme Court, according to former department attorneys.

This summer, Justice Department officials thought they had a candidate with the Mobile County school district, according to administration officials. But Michael Ross, an expert hired by the department, found that school officials were partly responsible for the failure to desegregate as many schools as they had promised, possibly violating the "good faith" standard and rendering the case unusable for a court test.

Charts and an affidavit submitted by Ross in U.S. District Court in Mobile last week state that school officials in Mobile incorrectly permitted a large number of white students to transfer out of the all-black or nearly all-black schools where they had been bused, even though few whites actually had changed their residences.

The Supreme Court never has defined a desegregated, or "unitary" school, according to civil rights lawyers. But the results-oriented standard commonly used in the past -- that school districts have a duty to eliminate all vestiges of state-imposed segregation and that the measure of a plan is its effectiveness -- came from language in Supreme Court school desegregation decisions from 1968 to 1979. Justice Department officials relied on the language in another Supreme Court case, Pasadena City Board of Education v. Spangler, to justify its new standard.

The department has succeeded in using its new standard in school desegregation consent decrees signed during the past year with school districts in Bakersfield, Calif., Lima, Ohio and Phoenix.

The decrees say that the school district will be removed from court order automatically if after three years the racially imbalanced schools reflect, within 20 percent, the systemwide racial enrollment.

If the schools do not reflect the systemwide racial percentages, the school district will achieve unitary status if it can show that it "fully and in good faith" implemented the plans in the consent decree. Such plans include the establishment of "magnet programs" to attract white students to schools with black children and vice versa.

But the Justice Department was unsuccessful in defending its new standard in Denver, where the issue was whether the Denver school district could be declared "unitary." The department argued that the Denver school district had achieved unitary status because it "fully and faithfully implemented a constitutionally acceptable desegregation plan" and because school officials had refrained from further intentionally segregative acts.

U.S. District Court Judge Richard P. Matsch in June disagreed with the department and school board's argument. "The measure of the adequacy of any desegregation plan is its effectiveness," Matsch wrote, adding that the faculty assignment desegregation plan in Denver was not effective, a problem that "by itself prevents the declaration that unitariness has been achieved."

During the first two years of the Reagan administration, the Justice Department agreed with Matsch. In a 1981 document filed in U.S. District Court in Mobile, for example, the department opposed the motion of the Mobile County school district to be declared "unitary" not only because "in some instances the projections of the decree were not met" but also because the decree was defective, leaving "12 predominantly all-black schools as vestiges of the prior dual era."

"Accordingly," wrote Assistant Attorney General William Bradford Reynolds, "even had the projections been substantially achieved, a unitary school district would not have resulted, for the plan failed to remedy the continuing constitutional violation found by the Supreme Court."

Justice Department spokesman Terry H. Eastland said the department decided to switch to the "fully and in good faith" language because the "notion of what constitutes a unitary school system has always been a subject of debate never settled within the courts" and because the old requirement -- to eliminate the vestiges of discrimination -- presented a problem.

"It was difficult to precisely define what the vestiges of discrimination were," Eastland said. "We had to define it."

The issue came about in this administration, Eastland said, because "a lot of school districts have been under court order for a long period of time." Without clarification of the old standard, Eastland said, the school districts might remain "eternally under court order."