Assistant Attorney General Benjamin R. Civiletti yesterday described as insignificant a contradiction between himself and a key aide about the dismissal of a U.S. prosecutor in Philadelphia.

Civiletti, testifying before the Senate Judiciary Committee on his nomination as deputy attorney general, outlined what he called his lack of involvement in the controversial ouster of U.S. Attorney David W. Marston. His apparent intent was to defuse a Republican attempt to use the confirmation hearings to focus public attention again on the firing of the Republican prosecutor.

Marston was dismissed after it was learned that Rep. Joshua Eilberg (D-Pa.) called President Carter last fall to urge his replacement. Marston said later that he told a Civiletti aide shortly after the Nov. 4 call to the White House that Eilberg was a potential target of an investigator by his office.

But Civiletti repeated yesterday that he had no recollection that the aide, Russell T. Baker Jr., passed the information on to him, as Baker claimed in a sworn affidavit.

"It appears to me it is an inconsistency without real substance or meaning," Civiletti testified. Eilberg was not a significant subject of investigation at the time, he said so there would have been no reason to warn Attorney General Griffin B. Bell or President Carter.

Sen. Strom Thurmond (R-S.C.), ranking minority member of the committee, started asking Civiletti about Justice Department procedures for dealing with sensitive investigations. The questions seemed to be trying to establish that Civiletti should have known and passed on even the fragmentary information about an investigation of Eilberg.

Yesterday's session was limited because of the Senate floor debate on the Panama Canal treaties. An unusual weekend committee meeting is scheduled for today to avoid further delays.

Sen. Malcolm Wallop (R-Wyo.) described as "superficial" in internal Justice Department investigation of the circumstances surrounding the Marston dismissal.

He also said there appeared to be "political overtones" to other recent Justice Department investigations, and he suggested that it might be necessary to appoint special prosecutors in some instances if Civiletti's answers didn't reassure committee members about the department's independence.

A Republican request to call several witnesses to testify about the Marston case has been shelved until the questioning of Civiletti is completed, several committee sources said.

The Republicans want to call Marston, Baker and White House aides Hamilton Jordan and Frank Moore, among others, to trace administration officials' knowledge of the dismissal. But Committee Chairman James O. Eastland (D-Miss.) has declined so far to approve the request.