A federal judge yesterday charged that Department of Defense officials acted improperly in using "technical" information from American Telephone & Telegraph Co. for a report on defense communications systems and then permitting the company to use the paper in its own defense against a Justice Department antitrust suit.

In a memorandum written by U.S. District Judge Harold Greene, AT&T personnel were cleared of wrongdoing in connection with the report, but Green sharply criticized the actions of attorneys for the Defense Department.

"Without making a determination whether any of these acts, standing alone, would have been improper, it is difficult to escape the conclusion that in the aggregate they amount to direct cooperation with a defendant in a lawsuit in which the government is the plaintiff, on the very subject of that lawsuit, and that on this basis they are not within the bounds of propriety," Greene said in the memo.

But Greene also noted that the information from AT&T in the study only contributed to one part of the document and that, even without the material, the Defense Department probably would have continued to oppose divestiture of the Bell System.

Therefore, Greene agreed to treat the report as evidence in the antitrust suit but said it is "entitled to less weight than would be a wholly independent, authoritative" DOD study.

Although Greene cleared AT&T officials of impropriety in connection with the paper, he did say that AT&T "may properly be faulted for continuing to argue and intimate in various ways" that Justice Department lawyers are not representing the Reagan administration officials.

The statement came a week after an unusual hearing called by Greene to investigate the circumstances leading up to AT&T's introduction of a Defense Department study. The paper concluded that the breakup of AT&T sought by the Justice Department in the case would harm the national defense communications system.

AT&T and DOD witnesses told Greene last week that on three occasions their representatives met at DOD suggestion to discuss AT&T network planning. Further, AT&T was the sole nongovernmental party to receive a copy of the paper for review, which ultimately was forwarded to an administration Cabinet-level group for use in telecommunications policy planning and was regarded as an authoritative position paper for top Defense Department officials. Defense Secretary Caspar Weinberger has urged that the suit be dropped.

Subsequently, a top AT&T official asked John T. Whealan, general counsel of the Defense Communications Agency if the paper could be used as evidence in the case, and Whealan approved the request.

Greene said the evidence "indicates that" DOD "relied almost entirely for the technical portions of its study upon AT&T" and said no one at DCA "seems to have the necessary technical skills to verify the accuracy of the data." Further, Greene said no higher-level DOD officials made "any substantial effort" to check the information.

"The document was simply forwarded to the Secretary of Defense and then to the president -- and similarly it was submitted for introduction into evidence -- on the basis of the data supplied by AT&T," Greene said.

AT&T lawyers have said on several occasions that the Justice Department actions are not consistent with opposition within the administration to the divestiture sought in the case.