The Supreme Court yesterday left untouched a massive school desegregation plan imposed on New Castle County, Del.

Over the dissents of three justices, who called the plan "more Draconian than any ever approved by this court," the court refused to review an order combining 11 independent school districts to remedy segregation in one of them, Wilmington.

The plan, implemented in September 1978 required the busing of about 21,500 students.

The manner in which the court rejected the case suggested continuing internal difficulties with the busing issue.

Three of the four votes required to review it were available from the dissenters, Justices William Rehnquist, Lewis Powell and Potter Stewart. dChief Justice Warren Burger said he thought it merited review but declined to provide the fourth vote because, he said, a "full court" was unavailable to hear the case.

That was an apparent reference to Justice John Paul Stevens, who said he did not participate in consideration of the Delaware case but did not say why.

Court observers could only speculate that Burger and the dissenters decided not to grant review for fear of the eventual outcome, which could make new law in the busing field.

Earlier this year, the court took another unusual action suggesting the justices no longer agree to hear busing cases.

In January, months after they announced they would hear a Dallas desegregation case, they said they had changed their minds and would not hear it.

In other action yesterday:

The court refused to consider a complaint by backers of Sen. Edward M. Kennedy that the Carter administration was improperly using the government to win the presidential nomination.

The court unanimously agreed that the government has no conflict of interest when it prosecutes a company for violations of child labor laws and then uses the fines collected for administration costs.

The case stemmed from a Labor Department investigation of "Jerry's," a Lexington, Ky., based fast-food operation that allowed 15-year-olds to work after 7 p.m. in violation of labor laws.

The department, under the law, can use the fines to reimburse its investigative costs. A lower court ruled that this could create "bias" in the department's enforcement process, just as financial profit for a judge who imprisons someone would create bias.

The justices said yesterday in Secretary of Labor vs. Jerrico's, the owner of Jerry's, that such reasoning did not apply in part because "no official's salary" or other personal benefits are tied to the fines.

The court ruled against the state of Louisiana in its effort to collect $107 million in interest from the federal government.The interest, the state contended, was owed because of offshore oil lease funds impounded by the United States during a dispute with Louisiana from 1956 to 1975. The courts settled the dispute in 1975 but the parties still fought over money.