Support for the D.C. voting rights amendment slipped to a razor thin margin in the Maryland Senate today, with the defection of one Baltimore senator. The measure had passed the Senate by a two-vote margin last session, but was killed in the House of Delegates after a bitter struggle.

"Sure, it'll be close in the Senate, when you have a two-vote margin and lose one of those," said the amendment's chief sponsor Sen. Edward T. Conroy (D-Prince George's). "But it will pass."

Still Conroy was concerned with the psychological effect of the senator's change of mind in this hardfought and emotional battle for ratification.

"Each time you lose one, it opens thedoor for the weaker supporters to say, 'Maybe we made a mistake,'" said Conroy.

This year, supporters' attention has been riveted on the House of Delegates, where several Jewish delegates have insisted they will not vote for the amendment unless D.C. Del. Walter Fauntroy agrees to criticize the Palestine Liberation Organization. Fauntroy declared Thursday -- two days after meeting with the delegates -- that he will not accede to their demands despite the fact that their votes may be crucial.

But the amendment will first come up for a vote in the Senate, where supporters were counting on 26 solid votes for passage.

Sen. Clarence M. Mitchell III (D-Baltimore), one of its staunchest supporters, was shocked when he learned that Sen. Cornell Dypski (D-Baltimore) had switched sides and voted against the amendment today in committee.

"He said yesterday he was voting for it," said Mitchell. I'm surprised, to put it mildly."

Mitchell accused Dypski of going back on an agreement made last session that Dypski would support voting rights if Mitchell helped kill another measure unpopular in Dypski's community.

"I feel that he's violated an agreement," Mitchell said.

Bridling at such a suggestion, Dypski replied, "I don't know where that has any reflection on my voting on this. I certainly never made a pact or agreement. What else did Mitchell say?"

Dypski insisted that he had changed his mind because the "more you read the U.S. Constitution, the more you can see that our forefathers thought Washington should not be a state."

The controversial amendment would give the District representation in Congress, including the right to elect two senators.

It has been the subject of a bitter battle in Maryland, which supporters had expected to make a showcase for their national ratification drive.

Several Jewish delegates -- who voted for the amendment last year -- have attacked Fauntroy for his meetings with the PLO last fall, and have refused to vote for the amendment. It was killed three times, each time by the slimmest of margins, in the House last year.

Despite the public attention on the House members, Sen. Tommie Broadwater Jr. (D-Prince George's) who carries a rollcall checklist in his pocket to count the amendment's support each day, said he has been concentrating on his Senate colleagues.

He says he has 24 "solid" votes necessary for its passage. "But when you need 24 and have 24 that doesn't give you any room to let up," he said.