The Justice Department internal investigators are seekiing sworn statements from President Carter and other top administration officials in connection with the controversial decision to fire U.S. Attorney David W. Marston of Philadelphia.

Most of the questioning appears to revolve around federal grand jury probes touching on Rep. Joshua Eilberg (D-Pa.), who got the President to agree last Nov. 4 to expedite Marston's removal.

The highly unusual in-house inquiry has already produced affidavits from Attorney General Griffin B. Bell and other high-ranking officials at Justice and a statement from the president that officials regard as sworn because it was obtained in pursuit of an investigation.

"We want to know what they know and when they knew it," said one Justice Department lawyer in words reminiscent of the key question underlying the Watergate scandal.

"It should be fairly obvious what's happening," said another official familiar with the process. "Let's assume for a moment that Marston was fired because of the Eilberg investigation. A crime may have been committed. Department regulations may have been broken. Or some ethical rule may have been violated. It's only logical to do this."

A Republican appointee who has been pressing investigations of official corruption involving Democratic officeholders. Marston was ousted Friday at a showdown meeting with Bell. The attorney general said he asked Marston to stay on the job temporarily but Bell also made clear, as Marston put it, that " the decision to fire me" was irrevocable.

According to White House press secretary Jody Powell, who was returning with the president from a weekend in Georgia. Carter was asked just one question: When did he first learn that federal prosecutors were interested in Eilberg?

Powell said the answer was: the day of the president's Jan. 12 press conference when Powell and Frank Moore, chief White House lobbyist on Capitol Hill, told him. It was at the press conference that the president touched off a storm by acknowledging that he had agreed to expedite Marston's removal at Eilberg's behest in a telephone conversation last Nov. 4.

Marston, it was learned, gave three high-ranking Justice Department officials sent to Philadelphia on Jan. 16 an affidavit stating that he told one of his superiors in the criminal division, Russell T. Baker Jr., of the Eilberg "problem" later in November. Baker has said he told his boss, acting Deputy Attorney General Benjamin R. Civiletti, the head of the criminal division, but Civiletti apparently cannot recall being so informed.

In any case, Bell and Carter added to the confusion last week. First the attorney general, at a Cabinet meeting on Monday, and then the President, at a meeting with junior members of the House on Tuesday, declared that the administration had not been "able to ascertain the existence of any investigation of Democratic congressmen" by the U.S. attorney's office in Philadelphia. Marston called the president's remakrs "flat, dead wrong."

The controversy centers on investigations of the construction of a $65 million addition to Philadelphia's Hahnemann Hospital. These have given rise to allegations that Eilberg and Rep. Daniel Food (D-Pa.) may have profited from the project.

The Justice Department inquiry is being undertaken by its Office of Professional Responsibility, which began collecting the statements early last week. They are expected to be submitted today to Solicitor General Wade McCree, the highest-ranking Justice Department official not involved in the internal investigation.

"He [McCree] may call for some additional work. Some things may need to be checked out further," said Justice Department spokesman Marvin Wall.

The head of the Office of Professional Responsibility, Michael Shaheen, said that if there are discrepancies, "we'll resolve them," but he declined to say if any had arisen at this point.

The President's brief statement was obtained last week by White House counsel Robert Lipshutz. Carter was apparently not asked to raise his right hand to make the statement a formal affidavit by swearing to it, but the Justice Department's Wall said last evening, "It's a binding statement, regardless of what form it's in."

One of those questioned, Civiletti, met with Marston and his staff in Philadelphia yesterday in an effort to assure them there would be no loss of momentum for their investigations. Civiletti disclosed to the staff that the in-house investigation was under way.

At least some of the Philadelphia lawyers were not reassured by the news. But a high-ranking Justice Department official in Washington said later he thought the inquiry a heartening sign. "In the past,"he said. "People would just have said, 'Forget about it.'"