The question was on education, and Rep. Barbara A. Mikulski (D-Md.) was ready.

"I'm glad you raised that question," Mikulski said at a recent candidates' forum at a Baltimore Democratic club, "because in the course of this campaign I have been subjected to a smear campaign by Mr. Michael Barnes . . . . "

Mikulski then stalked from behind the table where the other three Democratic candidates for the U.S. Senate -- Barnes, Gov. Harry Hughes and Baltimore County Executive Donald P. Hutchinson -- were seated. Shaking her fist, she said: "I gotta deal with this. My honor is at stake, and when it comes to Barbara Mikulski's honor, I'm not going to be quiet!"

Why was Mikulski so upset?

It was the persistent criticism by Barnes of her support for three amendments that helped private, and in some instances, segregated, schools keep their tax-exempt status. Barnes has been hammering away at those amendments as part of his strategy to win support in Baltimore's large black community.

Mikulski says that Barnes' attacks have been unfair.

"Don't let anyone, anywhere, tell you that Barbara Mikulski voted for segregated schools," she said. Her supporters point out that, unlike many other Democrats who came out of Baltimore's white ethnic political world, Mikulski was a civil rights activist. They say she should get credit for that.

Replied Barnes: "I didn't cast Barbara's vote for her. If we're talking about an inflicted wound here, we're talking about a self-inflicted wound."

The tax-exemption controversy started in 1970 when black parents in Mississippi went to court, declaring that segregated schools should not qualify for "charitable" deductions. The court agreed, and the Internal Revenue Service announced that it would begin denying tax-exempt status to schools that did not admit black students.

The schools fought the IRS, however, and the agency complained that the rules under which it operated were too limiting. The rules provided that, as long as a private school publicly disavowed discriminatory practices, it qualified for tax-exempt status, even if a court ruled that the school was in violation of the 1964 Civil Rights Act.

In August 1978, the IRS proposed a rule that it said would apply to only two categories of private schools: those under court order to desegregate, and those that were established or expanded in reaction to public school desegregation.

The proposed rule said such schools would have to prove that they were no longer discriminatory in order to get tax-exempt status. They would have to actively recruit minorities or have a minority enrollment equal to about 20 percent of the proportion of minority students in their community. That is, if minorities made up 30 percent of the community, then minorities should make up a minimum of 6 percent of a school's enrollment.

The agency said the proposed rule was designed to protect schools in largely white communities or Jewish and Catholic schools, all of which might not discriminate but might still lack minorities.

But the proposal generated a huge outcry, with critics saying that the IRS had overstepped its authority and was writing social policy. In Congress, those critics, led by the late John Ashbrook, a conservative Republican congressman from Ohio, introduced a series of amendments over the next two years to stop the IRS from depriving private schools of their tax exemptions.

Ashbrook said that the IRS had "confused its own role as a tax collector with that of a legislator, jurist or policy maker."

Ashbrook's amendments, attached to various one-year appropriations bills, stated that none of the money in those bills could be used to carry out any new IRS regulations or policies that would cause private schools to lose their tax-exempt status.

Reps. Louis Stokes (D-Ohio) and Charles B. Rangel (D-N.Y.), two senior black legislators, led the fight against the amendments, but the measures passed easily, especially the first three times. Rep. Parren J. Mitchell (D-Md.), admitting defeat even before the House vote, sarcastically chided members during the floor debate.

"The amendment is going to pass. It is going to pass overwhelmingly," Mitchell said. "Go ahead, pass it. I think it is an excellent time to pass this, when racial tensions are mounting in the country, when more and more blacks feel that the government is betraying them. Fine. Pass it."

The first vote occurred on July 13, 1979, and three others were in 1980: on June 18, Aug. 19 and Aug. 20. The Aug. 20 vote occurred because Ashbrook's amendment had to be rewritten to meet parliamentary objections of the chair.

According to the Congressional Record, neither Mikulski nor Barnes took part in the floor debate on the issue. Barnes voted against the amendment all four times. Mikulski voted for the amendment the first three times and against it the fourth time.

Mikulski said that she switched "If we're talking about an inflicted wound here, we're talking about a self-inflicted wound." -- Michael D. Barnes her vote -- a day after supporting the amendment -- because she received assurances from the IRS that the agency had no intention of going after the tax-exempt status of parochial schools, which are popular in her heavily Catholic district. She said she was concerned that the IRS rules were too broadly written.

An aide said Mikulski was waiting for Congress to complete a study on the IRS rule, and her votes were meant to delay implementing the rule until the study was completed.

Barnes said he never felt that Catholic schools would be threatened by the IRS proposal.

"My wife is a teacher in a Catholic school, so I am very sensitive to the issue," he said.

Whether Mikulski cast the right or wrong vote, got bad staff advice, or was confronted with a faulty IRS rule, it is obvious that Barnes feels he has found a hot issue and does not intend to let it drop.