Frederick and Crisfield broke open close games in the final period yesterday and scored 10-and 13-point victories to advance to today's championship round of the Maryland State basketball playoffs at the University of Maryland's Cole Field House.

Frederick outscored Cambridge-South Dorcester, 12-4, midway through the fourth quarter and came away with a 77-67 triumph in their Class B semifinal contest. Crisfield, leading by two with three minutes remaining, rode the foul shooting of guard Denny Laird to a 65-52 decision over Beall in Class C.

In today's title round, Frederick (25-1) meets Sherwood (22-4) at 1 p.m., and unbeaten Crisfield takes on Poolesville (16-9) at 6 p.m.

In other semifinal action last night, Surrattsville met Thomas Johnson in a Class A battle. Bladensburg tangled with Woodlawn of Baltimore County for a spot in the Class AA final.

Laird helped Crisfield rack up its 26th victory by converting three one-and-one situations in the final 2:13, as the Crabbers raised a 53-47 advantage to 59-49 with a minute left.

Beall (21-5) had pulled to within 49-47 behind five quick points by guard Marty Thomas, but the Mountaineers lost their chance to tie when Laird stole a pass and passed to teammate Johnnie Thomas for a breakaway layup to give Crisfield a 51-47 margin. The Crabbers upped the score to 53-47 on a basket by Jerry Carter.

Beall, which led by one at the half and trailed by one of the half and trailed by only two after a slow-paced third period, was forced to foul in the final 21 minutes, and each time picked the wrong man - Laird - to offend. The 5-foot-10 guard, who gave Beall a keep-away dribbling demonstration much of the second half, finished with nine points and was seven-for-eight from the foul line.

Carter, who scored 14 in the first half, led all scorers with 23 points. Marty Thomas paced Beall with 16.

In the Class B semifinal, guard Kevin Allen scored Class B semifinal, guard Kevin Allen scored 11 of his 17 points in the final quarter as Frederick handed Cambridge-South Dorcester its ninth defeat in 24 contests.

Frederick led 34-20 in the second period and seemed comfortably ahead, 40-34, at halftime before Keith Lee, the Cadets' 6-4 center who finished with 17 points, went to the bench after picking up his fourth foul after three and a half minutes of the third period.

When Lee - who scored 12 points and blocked five Cambridge shots in the first half - on the bench the rest of the period, the Vikings whittled away at Frederick's lead until two foul shots by Pat Chester put Cambridge up, 50-49, with 1:35 remaining in the quarter.

Lee and teammate Dane Dixon, who also missed much of the third quarter with four fouls, returned early in the final quarter to help close down Cambridge.