The head attorney for the U.S. Football League finished a grueling 13 1/2 hours of questions for National Football League Commissioner Pete Rozelle today in federal court.

But left unanswered, at least for now in the USFL's $1.32 million antitrust suit against the NFL, was the issue of whether the attorney succeeded in placing one of "three smoking guns" -- his theme during this trial -- in Rozelle's hand.

Rozelle ended 4 1/2 hours of questioning this afternoon -- his third day on the witness stand -- by once again denying knowledge of two interoffice memorandums written by NFL executives on the subject of the new league and of a Harvard University Business School seminar to examine a study of "how to conquer the USFL ."

But attorney Harvey Myerson, representing the USFL, spent much of his time in U.S. District Court trying to discredit Rozelle, once drawing NFL attorney Frank Rothman's ire for "yelling at the witness."

Rozelle will be cross-examined by NFL attorneys Tuesday. It is expected that Myerson then will call either NFL general counsel Jay Moyer, who wrote one of the memos, or NFL Management Council executive director Jack Donlan as a witness.

Apparently laying the groundwork for later witnesses in a trial expected to run into July, Myerson suggested to Rozelle that he had offered to give New York City a new NFL franchise in exchange for keeping the USFL's New Jersey Generals out of town.

"If anyone says that, they are lying, because I never said that to anyone," Rozelle said, jabbing his finger at Myerson in their most pointed exchange of the week-old trial.

Myerson harked back 27 years, to the days when Rozelle was general manager of the NFL's Los Angeles Rams, to recall a potential embarrassment for the commissioner, who has criticized the USFL for signing undergraduates such as Herschel Walker.

Under heavy questioning, Rozelle said he signed coveted Louisiana State running back Billy Cannon more than a month before Cannon's last college game in the Sugar Bowl. The signing was not disclosed until after the game, for which it should have made him ineligible.

When he signed, Cannon was registered in the Philadelphia Sheraton under the name "Billy Gunn," at Rozelle's suggestion, Rozelle confirmed. "I did it to protect Billy Cannon," Rozelle said.

The Rams lost Cannon to the AFL's Houston Oilers, who also signed him prematurely, Rozelle said.

Myerson introduced into evidence the minutes of an NFL owners meeting and a case study by Harvard Prof. Michael Porter, who led the February 1984 Harvard seminar attended by 65 NFL officials.

"I didn't have anything to do with it and I don't think anyone in the league office had anything to do with it either," Rozelle said.

Myerson then introduced the minutes of an October 1983 NFL owners meeting in New York that recorded the commissioner as saying the league office and Management Council would initiate seminars to deal with "finances, player personnel, labor, etc."

Rozelle said there was no connection between those seminars and the Harvard seminar arranged by the Management Council.

Myerson also introduced a case study by Porter that Rozelle said he "glanced through" during a 30-45 minute meeting with Porter over a drink in June 1985.

"The only reason I met with Mr. Porter was as a favor to a friend," said Rozelle. "I did not read the material. I glanced at it."