If the case were a Broadway production, it could have won a Tony award for the longest-running play in American stage history, with the fastest-changing cast of supporting characters.

After 15 years of court orders and consent decrees, Justice Department lawyers are asking a federal judge to bring down the curtain on the convoluted civil rights case known, for the time being, as Adams v. Bell. At issue is the Reagan administration's record in desegregating southern schools, as well as the larger question of whether the judicial branch can tell the executive branch what to do and when.

The administration's request comes when the Justice Department has entered other cases -- involving Little Rock and Norfolk school districts -- to try to halt court-ordered desegregation plans that it views as excessive. To civil rights groups, the actions, taken together, appear to signal a historic reversal in the federal effort to force the desegregation of America's schools.

The Adams suit began in 1970, when the NAACP Legal Defense and Educational Fund Inc. asked U.S. District Judge John H. Pratt here to force the Nixon administration to threaten to cut off funds to southern school districts that discriminated against black children. Women's groups later joined in the suit, followed by groups representing handicapped students, and then Hispanic students. As the original plaintiffs left school, new students were added to the case.

In 1977, Pratt established strict timetables for the government to resolve civil rights complaints filed against school districts, then modified them slightly in 1983.

The Reagan administration, however, is arguing that it has stepped up its efforts to enforce discrimination laws, and that there is no need for continuing judicial oversight. It says that since it took office, the Education Department has initiated 43 cases against 41 school districts; cases against 23 districts are pending before Education Department administrative law judges, while the other 18 have been referred to the Justice Department for further action.

Before Pratt's 1977 order, it noted, the Office of Civil Rights of what was then the Health, Education and Welfare Department had initiated 46 enforcement proceedings, but all of them dealt with sex discrimination in school athletic facilities. The 23 cases initiated by Harry M. Singleton, assistant secretary of education for civil rights, that are pending before the department include eight cases of racial bias, nine of bias against the handicapped and six are sex-discrimination cases. Justice officials would not describe their pending cases.

"The conscious policy of non-enforcement of the early 1970s no longer exists," the government said in court papers, "and has not for a number of years. Indeed, the present assistant secretary of education for civil rights has caused more enforcement proceedings to be commenced than have all preceding assistant secretaries . . . . "

But the NAACP Legal Defense and Educational Fund Inc. contends that the administration initiated those actions only because Pratt's timetables forced it to. Once the suit is dropped, the fund's lawyers argue, the administration will revert to the "non-enforcement" policies of the Nixon era.

The administration also has argued that Pratt's timetables are too restrictive. Under the judge's order, once a complaint is filed, the department has 90 days to determine whether discrimination has occurred, then the school district must correct the situation within another 90 days. If the problem is not corrected by then, the department must impose sanctions within one month.

The Reagan administration has called the time frames "disruptive, costly and counterproductive for efficient and effective civil rights enforcement . . . . Rigid deadlines . . . create an incentive to process easy cases first, and result in a high error rate."

The Adams case has consumed hundreds of thousands of pages in almost as many pleadings. It has continued through four administrations -- and the creation of the independent Education Department.

Now there is a new twist: citing a recent Supreme Court ruling, government lawyers are preparing to argue that the original plaintiffs in the case -- Kenneth Adams and his brothers and sisters who went to segregated schools in Quitman County, Miss. -- are no longer qualified to sue, because they have not suffered direct harm.

Last July, in an unrelated case involving the tax-exempt status of private schools that are found to discriminate, the Supreme Court suggested that plaintiffs in future discrimination cases might have to show that they suffered "direct harm," particularly when their complaint is with some institution and not the government.

"The government has gotten very technical," said Elliott Lichtman, the latest lawyer handling the case for the NAACP legal fund. "They are unable to win on the merits, so their tack is to try to undermine the merits by challenging our plaintiffs' " right to sue.

Most of the children named in the case attend schools in two South Carolina school districts, two North Carolina districts, and one in Mecklenberg County, Va., where they attend integrated schools but attend classes of all-black students because the schools divide students according to their "class performance."

The remaining plaintiffs are college students. The state of Virginia is accused of reneging on promises to upgrade the historically black Virginia State University, while the historically white University of Arkansas is targeted for not doing enough to recruit black students.

The government has asked that the strict timetables be lifted until the issue of the students' standing to file suit is resolved. An appeals court has returned the case to Pratt for resolution of that issue.

In mid-January, Pratt gave the government two months to complete its exploration into the standing of the plaintiffs.