Fourth-ranked Bladensburg sank 12 free throws in the fourth quarter, two by Willie Swearing with 36 seconds left, to sink 10th-ranked Potomac, 85-83, in the Maryland Class AA Region III title game yesterday at Prince George's Community College.

The Mustangs (22-1) advance to the state semifinals Friday at Cole Field House against the Baltimore County champions.

As it has done all season, Bladensburg dominated the backboards, 58-40. The Mustangs converted 13 baskets following offensive rebounds.

Skip Speaks scored eight points while teammates Bryant Thornwell and Levi Morton added six and five points, respectively , in the decisive fourth quaret.

Potomac (20-5), the state AA runner-up last year, was never in the game after the first period until Tony Dawson rallied the Braves from a 10-point deficit.

Ten points by Dawson and two baskets from Mo Rivers brought Potomac to within three points, 82-79, with 37 seconds to play.

Swearinger, the quick, 5-foot-8 point guard, dropped in two free throws before Potomac's Rennie Robinson and Leo McGainey sank consecutive jump shots to narrow the gap to 84-83 with nine seconds left. The Braves got their opportunity to get that close only because of some erratic and unwise play by the Mustangs.

Nursing a five-point lead with a minute to play, Speaks threw up two long attempts, which Potomac rebounded and converted into baskets at the other end.

"I told them to take the shots," said Bladensburg Coach Ernie Welch. "Potomac is so quick, I'm not sure we could have gone to four corners and held the ball."

After McGainey's basket, Charles Sawyer dropped in the front end of a one-on -one foul situation to give Bladensburg a two-point lead. The Mustangs then backed away as Potomac rushed up court for a tieing attempt. McGainey was not contested as he grabbing 19 rebounds and Morton and the ball fly. The sophomore's 17-footer was short and Bladensburg was the winner.

The Mustangs, with Thurl Bailey grabbing 19 rebounds and Morton and Thornwell adding 11 and 10, respectively, broke away from a 19-19 first-period deadlock to lead by as many as 14 late in the third quarter, 58-44.

The smaller Braves were unable to keep the physical Prince George's AA League champions off the boards and had little choice but to surrender lay-ups.

"All year long, we've been able to control the boards," said Welch.