The Justice Department is investigating irregularities in the financing of Pennsylvania Gov. Milton Shapp's 1976 presidential campaign for possible criminal violations of federal law.

The probe stems from a recent finding by the Federal Election Commission that Shapp's campaign organization made incorrect claims about its fund-raising activities during the governor's short-lived bid for the Democratic presidential nomination, sources confirmed yesterday.

As a result of the FEC finding, Shapp has been required to return $299,066.21 in federal matching funds that this campaign received.

The sources said the criminal probe is still in a very preliminary state and has not proceeded much beyond investigation and collection of evidence by FBI agents working under Justice Department direction.

The aim, the sources said, is to determine whether any persons, including Shapp, engaged in a conspiracy to violate federal laws knowingly.

The evidence collected will almost certainly be presented to a federal grand jury in Pennsylvania, the sources said. But they denied reports that a special grand jury already has been empaneled in Philadelphia or any other Pennsylvania city.

Although personnel from the three U.S. attorneys' offices in Pennsylvania have been involved in the probe, the sources said, it is being coordinated from Washington by Craig Dansanto of the Justice Department's Public Integrity Section. That section is a branch of the Criminal Division. It was established early last year to investigate allegations of wrongdoing by public officials.

In Harrisburg, a spokesman for Shapp said the governor felt he had nothing to fear from any investigation, and added that Shapp and his staff would cooperate fully with any federal inquiries.

The case arose from a requirement in the federal election law stating that a candidate must raise at least $5,000 in 20 different states to qualify for matching federal funds. These $5,000 minimums must be made of individual gifts not exceeding $250 each.

Although Shapp certified that he had met this requirement, the FEC found that his campaign organization had failed to raise the funds properly in five states. Instead, the FEC said, contributions by individuals in excess of $250 were masked by having them made through friends or employees of the contributor.

Following the FEC finding, Shapp said he would voluntarily repay the federal funds he received. But he has denied any personal knowledge of improper activities in collecting the contributions.