Supreme Court Justice William H. Rehnquist must smile at times when he hears the latest policy reversal of the Reagan administration Justice Department. Some of the strong dissents he has written in key cases in recent years now seem to be providing the intellectual underpinning for the new government policies, especially in the civil rights area.

For instance, when the administration reversed the long-standing Internal Revenue Service policy against granting tax exemptions to segregated private schools last month, its legal analysis cited Rehnquist. He argued last year against the court's refusal to review a claim by the segregated Prince Edward (Va.) School Foundation, saying the IRS' authority in denying exemptions "is not apparent" from reading the law.

Similarly, when William Bradford Reynolds, who heads Justice's Civil Rights Division, said he was looking for a case to overturn the Supreme Court's landmark affirmative action case, Weber vs. U.S., which approved voluntary private agreements to increase the black work force, it was clear that Rehnquist's lengthy dissent had become the administration position.

Recent school desegregation cases show Rehnquist and the administration of like mind in their opposition to busing as a remedy.

It is not surprising that Rehnquist's dissents have found a home. President Reagan's campaign speeches incorporated some of the themes that the conservative justice has outlined in ringing minority statements--including stands against busing and quotas.

In fact, the Rehnquist view is increasingly becoming the majority viewpoint at the court. With the new administration, some consider him the controlling force among the justices.

Reynolds said, "It's what one might have expected. This administration is much more in line with Rehnquist than with Brennan." Justice William J. Brennan is considered the leader of the liberal wing of the court.

Some Justice attorneys have grumbled about what they see as a "Rehnquist connection" at the department. Former Rehnquist clerk Charles J. Cooper is a Reynolds aide, and John G. Roberts Jr., another Rehnquist clerk, is a special assistant to Attorney General William French Smith.

Others are troubled mainly by the boldness with which the new administration has announced its intentions to move the law toward its point of view.

William L. Taylor of the Leadership Conference for Civil Rights said Reynolds' approval of a desegregation plan without busing students in Chicago ignores Supreme Court precedents. "I think his action is in conflict with his oath of office," Taylor said. He noted that at least two Supreme Court cases have said that "freedom-of-choice" remedies in school cases are not adequate.

One Justice attorney said the department's pronouncements "feed disrespect for the court." In the tax-exemption and affirmative action cases, especially, this lawyer said, the administration could take its legitimate disagreement to Congress without trying to undermine court precedents.

The administration's positions have been challenged from within. Half the lawyers in the Civil Rights Division, for instance, recently told Reynolds flatly that they consider his stand on the tax-exemption issue a violation of the law.

Constitutional scholars, on the other hand, seem largely undismayed.

Paul Freund, a Harvard law professor and Supreme Court expert, noted in a phone interview from Boston that dissents traditionally have become the basis for change. Justices Oliver Wendell Holmes and Louis Brandeis were cited during the New Deal to support changes in government policy, he noted.

Because dissents often have "long-range, germinal influence," Freund said, "maybe Rehnquist will become the Oliver Wendell Holmes of his generation."

"What's unusual in this administration is that the government had prevailed and is now seeking, in a sense, to cast off those victories," he said.

A. E. Dick Howard, another Supreme Court watcher who teaches law at the University of Virgina, said his impression is that the Reagan administration is attempting to push its cause "as far as the Constitution will permit."

So far, he said, the pushing "seems within the permissible bounds of debate. I may quarrel with some of the specifics, but they're not striking at the foundations of the Republic."

Howard added that the Reagan administration has been "invited to take advantage of the court's lack of clarity" in recent key cases. He noted the justices were sharply divided on the Weber affirmative action case, and that recent school desegregation cases have been "as murky as the Potomac."

Philip Kurland, of the University of Chicago law school, and William Van Alstyne, a Duke University law professor teaching at Berkeley this semester, agree.

Kurland said split judgments by the court invite Reagan officials to do what they're doing--"working around the fringes." He didn't think the administration should take Weber and the tax exemption cases to Congress for redress. "There's a problem there with the law of inertia, getting Congress to move."

Van Alstyne said, "It's not improper for the executive branch to display a good deal of discretion" in how it disperses its resources in enforcing the laws. But he said he was puzzled by Reynolds' stated desire to overturn the Supreme Court's Weber decision. "That is the law," he said. "It is foolproof against litigation to stop it."