D.C. City Council Chairman Sterling Tuckers appears to be having trouble holding on to his support from ministers in his campaign for mayor in the Sept. 12 Democratic primary.

On May 22, Tucker announced the support of a coalition of 71 churchmen. Within a week, however, two said they favored no candidate, one other announced support for Mayor Walter E. Washington and still another cautioned that his support was only conditional.

Now comes disclosure of a letter to Tucker from Canon Lloyd S. Casson of Washington Cathederal, who had also been included in the Tucker supporters announced in May.

"Dear Sterling," Casson wrote May 24, "Just a note to confirm the conclusion of our telephone conversation yesterday, that you will remove my name from any list of supporters for your candidacy for mayor.

"I would prefer to be not publicity identified with any particular political canpaign or candidate.

"Thak you for your understanding of this matter. Peace. (Signed) Lloyd."

Bishop Samuel Kelsey of the Temple Church of God in Christ was on the list of Tucker supporters but later announced that he was backing the mayor.

The Rev. Robert L. Pruitt of Metropolitan AME Church and the Rev. Jerry A. Moore Jr. of Nineteenth Street Baptist Church (the sole Republican on the City Council) said they had not been notified that their names would be on the list of Tucker supporters and declared they were neutral.

The Rev. Leamon White of Mount Bethel Baptist Church said his support for Tucker is conditioned on future statements by the candidate on the issue of legalized gambling in the city.

A year ago, when D.C. Corporation Counsel John R. Risher Jr. took City Council Chairman Sterling Tucker to court, some said that such high level legal infighting in the city's young home rule.

But Risher, who earlier this week announced that he will resign from office June 25, said he has never seen it that way.

"Hell," he said casually the other day, "that's the same thing I heard people saying about why we shouln't get upset because of what (former President) Richard Nixon was doing."

"That argument," Risher said, is "sort of a subtle, mindless statement that sounded pretty much like this: There are very few black leaders in the city. You challenge one of those black leaders and you're gonna lose what you have received by the grace of Congress."

"I don't buy that," said Risher, who is black. "I don't think that's what the people of the city think. I don't think that's what the Congress thinks.

Risher had asked the court to remove Tucker from office on grounds that the council chairman violated the city's home rule charter by teaching part-time at Howard University.D.C. Superior Court Chief Judge Harold H. Greene ruled that Risher's charges were warranted, but said that removing Tucker from office because of the violations would be too harsh a punishment.

A new move is one to draft former D.C. School Superintendent Barbara A. Sizemore as a candidate in this fall's elections, but Sizemore, who still negotiating a contract ot become superintendent of the schools in Benton Harbor, Mich., said she wants no part of it.

The move is being led by Nelson Terry of the Bloomingdale Civic Association, which represents an area in Norteast Washington near McKinley High School. Terry supported Sizemore in her narrow defeat in the July 19, 1977, council election.

Terry is soliciting money and volunteers for work in a campaign by Sizemore, who months ago said in an interview that she does not want to return to the local political arena.We can get Barbara . However she feels that a campaign cannot be run without money.We believe that if we can eliminate the need for Barbara toworry about resources, she would be open to a draft movement, Terry writes in an open letter to potential supporters.

Not so says Sizemore. "I'm not going to run, she said last week. I'm just not ready to come back to D.C." Why? "For a lot of reasons, mostly all personal."