Jim Lynam, fired in March as coach of the Los Angeles Clippers, has landed another NBA job, as a Philadelphia 76ers assistant under their new coach, Matt Guokas. Lynam, an old Philadelphia hand, coached St. Joseph's there after a stint at American University here . . .

Oliver Purnell has joined Lefty Driesell's University of Maryland staff, filling the vacancy left when Sherman Dillard opted to be a University of California assistant under his old coach at James Madison, Lou Campanelli. Purnell, an assistant at Old Dominion since playing point guard there 1971-75, is reputed to be an excellent recruiter . . .

The Atlantic 10 Conference has voted to do away with the three-point field goal. League directors, convened in Hasbrouck, failed to reach a decision on where to hold its postseason men's basketball tournament, a league spokesman said.

The directors of the league did decide sites for 10 of 11 championships during the 1985-86 academic year and selected Larry Weise of St. Bonaventure to replace Frank McInerney of Massachusetts as president of its board of directors. Joining Weise on the new board will be Mike Schultz of St. Joseph's, vice president, and Steve Bilsky of George Washington, treasurer.