A federal judge has enjoined the Buffalo Evening News from giving away more than two free Sunday editions of the paper to subscribers. The News had planned to give away a free Sunday paper for the next five weeks, in order to introduce its new Sunday edition.

The Buffalo Courier Express, the News' morning competition, had filed a suit in federal court in Buffalo charging the News with trying to put it out of business.

The Sunday Courier Express is responsible for 61 per cent of all of that paper's revenues. It had had no competition in recent years. The Courier Express had asked the court for a temporary injunction to preven the News from giving away Sunday papers.

In a 48-page order issued last night, U.S. District Court Judge Charles Brieant granted parts of the Courier Express request and rejected others, pennding trial of the matter.

He said the News could give away free samples during the next two weekends, without charge, but any Sunday editions after November 25 "must be sold for no less than 30 cents" - the proposed cover price for the new Sunday News, which is 20 cents lower than the Courier Express Sunday paper.

Judge Brieant also said the News had to withdraw its promise to potential advertisers that the first five Sunday papers would reach "280.000 subscribers." He ruled that advertisers who had cancelled advertising in the Sunday Courier Express in anticipation of going over to the News could cancel their News ads in any or all of the three Sunday editions that will no longer be free.

In an unusual ruling, Judge Brieant barred all news employees, including paperboys, from "predicting to any person the insolvency, bankruptcy, or discontinuance of publication of the Courier Express, or starting rumors or otherwise interfering with the Courier-Express' contractual or employment relationships while this litigation is pending . . . not even in jest."

Michael Trimboli, one of the Courier Express attorneys, said he was happy with the ruling, but "we wish it would have been for everything we asked."

The Evening News was purchased last April by Blue Chip Stamps, Inc., for about $37 million. Blue Chip is controlled by Warren E. Buffett, of Omaha. Nebraska, who also owns substantial stock interests in The Washington post Co.