The National Football League has withheld approval of a free-agent contract signed by defensive lineman Dan Sileo and placed the former University of Maryland and Miami player in a supplemental draft scheduled for Wednesday.

Sileo, a 6-foot-2, 282-pound nose tackle, signed with the Tampa Bay Buccaneers last Sunday, two days after the NCAA ruled he could not play at Miami this season because the five-year period he had to complete his college eligibility expired after the 1986 season.

The Buccaneers released a statement from club counsel Richard McKay: "The Buccaneers are very disappointed in this action taken by the National Football League in disapproving this contract which complies with the rules set forth in the Constitution and bylaws of the NFL.

"We have yet to receive any satisfactory explanation as to why the contract has been disapproved and thus will take any action necessary to preserve our contractural rights with Dan Sileo." . . .

Brian Bosworth, the Seattle Seahawks' $11 million rookie linebacker, plans to take the NFL to court, his agent says. New York-based Gary Wichard says he plans to file a lawsuit next week against the NFL on Bosworth's behalf so that Bosworth can wear No. 44, his number at the University of Oklahoma.

Bosworth refused to criticize the NFL on Thursday after he was forced to switch from No. 44 to 55 by league officials. League rules say linebackers must wear numbers in the 50s and 90s. Bosworth will wear No. 55 when the Seahawks open their regular season in Denver today. Seattle Coach Chuck Knox has named Bosworth as a starter.