The Carter administration's continuing problems with the U.S. attorney's post in Philadelphia continued yesterday as Samuel Dash, former counsel to the Senate Watergate committee, withdrew as a candidate for the job.

Dash, now a law professor at Georgetown University, said in a phone interview yesterday that he changed his mind about being available for the prosecutor's job because Attorney General Griffin B. Bell's delay in naming him raised conflicts with other pressing commitments.

Dash had been Bell's announced choice to replace Republican David W. Marston, whose dismissal in January touched off a national furor.

Marston said that a call to President Carter from a Democratic congressman led to his firing. The congressman, Rep. Joshua Eilberg (Pa.), was a potential target of an investigation by Marston's office at the time, Marston said.

The circumstances of the dismissal led to calls for an investigation of possible obstruction of justice by Bell and Carter.

Though Dash was Bell's first choice as a replacement, the attorney general began to hesitate after reports that Dash had been a character witness for a St. Louis attorney who reportedly had ties to organized crime.

On Feb. 13, Dash wrote Bell that he was withdrawing, but left open the possibility that he might reconsider.

Bell met with Dash yesterday morning, but failed to change his mind.

Bell was effusive in his praise for Dash in a statement he issued to announce the withdrawal. He called Dash "eminently qualified," and said he would have made "an exemplary prosecutor." He added that he hoped Dash could be persuaded to return to public life in the future to "further his already illustrious career."

Specific reason for the more than one-month delay in naming a permanent replacement for Marston were unclear yesterday.

Bell indicated in remarks to some reporters at the Justice Department yesterday that he was not concerned about the reports questioning Dash's judgment in testifying for Morris Shenker, an attorney who was counsel to Teamster Union boss Jimmy Hoffa.

He suggested that one reason for the long delay was his hope to name all three Pennsylvania U.S. attorney candidates at once.

But others, including Dash and Jerome Shestack, a Philadelphia attorney who headed Bell's personal search committee for a Marston replacement, said they felt the attorney general might be holding off a decision until completion of confirmation hearings on Benjamin R. Civiletti to be deputy attorney general.

Republican members of the Senate Judiciary Committee have used the Civiletti hearings to examine the Marston dismissal in great detail.

Shestack said in a phone interview yesterday that "maybe the judge [Bell] feels it is prudent to wait until the hearings are finished and everyone has had their chance to take a potshot at everyone."

Dash said only that Bell told him in confidence that part of the reason had to do with "internal Justice Department matters." Bell said later, through a spokesman, that he didn't know what Dash meant by that.

Department officials said yesterday that Bell would be in no rush to pick a new candidate because the Philadelphia office wass functioning well under an interim U.S. attorney.

Marston's predecessor in the post, Republican J. Clayton Undercofler III, has been the only other candidate interviewed so far, a spokesman said. The Shestack committee had recommended three other persons too, but the spokesman said Bell had no plans now to interview any of them.

Other persons within the department have been mentioned as candidates for the Philadelphia post, including John M. Dowd, an organized crime strike force prosecutor who is now investigating Eilberg.