The Reagan administration has decided not to appeal a U.S. district court ruling that limits the government's ability to enforce laws against sex discrimination at schools.

Womens' groups immediately attacked the decision as a "disgrace" and a significant shift in government policy. But William Bradford Reynolds, head of the Justice Department's civil rights division, said the ruling "is pretty sound as a matter of law," so the decision against an appeal is not a policy shift.

The July ruling by District Court Judge D. Dortch Warriner in Richmond said that Title IX of the 1972 Education Act amendments, which prohibits sex discrimination in federally funded education programs, doesn't apply to the University of Richmond's athletics because the sports programs themselves don't receive any federal funds.

The university did receive a $1,900 federal grant for its library, but Warriner said that was no excuse for the Education Department to "take the law into its own hands" with a broad view of its enforcement authority. The judge said the department could not even investigate possible discrimination in programs that didn't receive funds from the government.

The Supreme Court has never addressed the question directly, but if Warriner's ruling is upheld, civil rights attorneys said, it would undercut the government's ability to enforce civil rights laws in the nation's college athletic programs. "We'd only be able to investigate about one-half a percent of the schools--those we built gymnasiums for," a government lawyer said.

Until the Reagan administration took office, the government took a broad view of Title IX, saying it applied to all of a school's programs if it received even a dollar of federal aid. As a result, colleges began taking steps to put their athletic programs for women on a more equal footing with those for men.

Reagan Education Department officials, such as general counsel Daniel Oliver, have been urging for months that the government take a narrower view of the law. Until now, however, Justice Department officials haven't gone along.

Solicitor General Rex E. Lee at Justice, who is in charge of arguing the government's side in such cases, said yesterday, "I give heavy deference to the policy-making agency" in decisions not to appeal. Reynolds told United Press International that the Education Department didn't want to appeal, and Justice officials saw "no overriding reasons" to push the case.

Last month, Clarence M. Pendleton, the new chairman of the Commission on Civil Rights, signed a letter from the commission warning Attorney General William French Smith and Education Secretary Terrel H. Bell that the Richmond ruling "would decimate civil rights protections in education" if not reversed.

But yesterday Pendleton said in a telephone interview from California, "I'm of the mind that Brad Reynolds is looking very hard, looking where to really make a stand on this issue, and maybe there's another case that's better." Pendleton said "we'll have to wait and see" the effects of the government decision because there are conflicting court rulings in other parts of the country.

Last month, the 3rd U.S. Circuit Court of Appeals in Philadelphia ruled that Title IX protections did apply to Grove City College in Pennsylvania even though its only federal aid was in the form of student grants and loans.

Dorothy Ridings, president of the League of Women Voters, said yesterday her group was "severely disappointed" by the administration's decision not to appeal the Richmond case. "It's a major setback to civil rights enforcement," she said. "It tells us we've got a lot of trouble with Title IX in this administration."

Margaret Kohn, of the National Women's Law Center, said the administration's decision "is a disgrace. It doesn't square with a strong enforcement posture. It is inconsistent with the position they've taken in other cases, like Grove City. It calls into question their commitment to enforcement."

The Richmond judge issued a very broad injunction against the government, Kohn said. "It's hard to believe the administration couldn't have appealed on any of a number of grounds. . . . To me, this was a highly political decision."