Both the Energy and Justice departments reported to President Carter yesterday that they could find no evidence oil companies acted together in any way to cause or to worsen last year's gasoline shortages.

The shortages instead were the direct result of a drop in U.S. oil imports in the wake of disruption of Iranian oil production, the DOE report said.

There were a number of other contributing factors, DOE officials said, including the relatively low level of oil stocks late in 1978, fear about future availability of crude oil and the way DOE's price and allocation regulations made it more difficult for companies to adjust to sharply altered circumstances in the domestic oil market.

The two reports reached the same conclusion as that of preliminary studies completed about a year ago. However, at the time, the DOE study was labeled a "white wash" by some oil industry critics.

The Justice report said its investigation "has not disclosed any basis for instituting an enforcement action under the antitrust laws in this area." In other words, there were no indications of collusion on the part of the oil companies to warrant an investigation that could lead to possible prosecution.

Thomas Newkirk, DOE deputy general counsel for regulation, said the departments had sought evidence of an oil industry conspiracy. "We have looked and have not found evidence to support it," he declared.

Douglas Robinson, deputy administrator of DOE's Economic Regulatory Administration, said even the oil companies that behaved in the most conservative way -- lowering refinery operations to conserve crude oil stocks while not drawing down gasoline inventories as much as DOE thought they safely could -- had "a plausible reason" for acting as they did.

"It was purely a question of judgment at the time," he said.

One industry critic, Edwin Rothschild of Energy Action, a consumer-oriented group, remained unconvinced by the two reports. Rothschild complained the two departments still had failed to examine major oil companies' internal documents regarding the shortage. In particular, he said, Justice had not compelled some oil companies to produce documents showing why they built up gasoline inventories during the shortage period.

According to the Justice report, however, a significant portion of its study was based on a detailed questionnaire sent to the 25 largest oil companies, the responses to which were returned along with sworn affidavits attesting to the accuracy of the information provided.

Justice and DOE also used oil data regularly provided to the Energy Information Administration.That information was checked by both DOE auditors and an independent public accounting firm.