After being attacked by civil rights groups for trying to remove the ban on tax exemptions for private schools that discriminate against blacks, the Reagan administration is now under attack from the opposite end of the political spectrum for retreating and reversing itself on the issue.

Representatives of the religious right told top White House aides Tuesday that they will oppose the administration's proposed legislation that would reinstate and reinforce the tax exemption ban, and they warned that President Reagan's flip-flop on the issue was eroding his political base.

Some civil rights leaders say that no bill is necessary because existing Internal Revenue Service rules already bar discrimination.

Several participants at the White House meeting complained that the administration aides present--including counselor Edwin Meese III, domestic policy adviser Martin Anderson, White House counsel Fred Fielding and Deputy Attorney General Edward C. Schmults--just didn't seem to understand their concern that religious liberty, as well as racial discrimination, is an issue in the bill.

They said that William B. Ball, an attorney who is representing Bob Jones University before the Supreme Court in its challenge to the IRS's revocation of its tax exemption, called the bill "blatantly unconstitutional" because it wouldn't cover schools whose discrimination is based on religious beliefs.

The administration aides made no commitment to address the groups' concerns, participants said. "The administration feels boxed in," one said. "It feels it has to come out with a great display of nonracism and support this bill."

Paul Weyrich, head of the Committee for the Survival of a Free Congress, said the group reminded the Reagan aides that it was the Christian schools' battle with the IRS over tax exemptions, not abortion as is generally perceived, that prompted such groups as the Moral Majority to take an active part in the 1980 election.

Connaught Marshner, of the Pro-Family Coalition, said conservative religious groups thought the administration's Jan. 8 announcement that the IRS would no longer bar exemptions for discriminatory private schools "was too good to be true."

After the administration retreat, "we're worse off than when we started," she said.

Marshner and Bob Baldwin, of the National Association of Concerned Parents and Educators, said most Christian schools don't discriminate, so the bill amounts to using "a cannon to get a mosquito."