Pat Williams, general manager of the Philadelphia 76ers since 1974, will become president and part-owner of a group hoping to bring an NBA expansion team to Orlando, according to a report in the Orlando Sentinel. An official announcement will be made at a news conference today, according to the newspaper.

"My gut feeling is that the Orlando offer is too good to turn down," 76ers owner Harold Katz told the newspaper. "It's a once-in-a-lifetime offer, and as Pat's friend, I can never ask him to turn down something that good."

Williams' replacement in Philadelphia is expected to be John Nash, the team's assistant general manager and business manager . . .

Wayne Embry will be named the general manager of the Cleveland Cavaliers today, and the former NBA player and executive then will hire Willis Reed as his head coach, it was reported.

A source close to the Cavaliers told United Press International that Embry, a consultant with the Indiana Pacers, has stipulated he must be able to hire Reed, an assistant coach with Atlanta.

A Cavaliers spokesman would not comment, but said the team is planning a news conference for this afternoon . . .

In Milwaukee, the Common Council has reached agreement with developers of a new downtown sports arena.

The council approved an agreement with the Bradley Center Board after months of talks. A contract for land acquisition can be terminated if developers and the city do not reach accord on such matters as land use and parking space by the end of the year.

The Milwaukee Bucks had hoped to move to a new facility in time for the 1987-88 season. The proposed construction timetable could delay the move to autumn of 1988, spokesmen said.