Jay Colbert stands 5 feet 7 1/2 inches tall. He weighs 180 pounds. Although he is smaller than most players, the senior running back is breaking some of the biggest marks in the Gaithersburg football record books.

One week after setting a record for career rushing yardage, Colbert set a single-game mark with 256 yards and three touchdowns, helping the No. 4 Trojans remain undefeated with a 31-12 victory over host Churchill last night in a Montgomery 4A game before 1,200 in Potomac.

Colbert scored on runs of 72, 1 and 77 yards in helping Gaithersburg (6-0 overall, 6-0 league) to a 21-12 halftime lead.

"He is just a great, great back; he turns chicken salad out of chicken manure," said Gaithersburg Coach John Harvill, whose team has won 12 consecutive regular season games. ". . . It was a pretty good night, wasn't it?"

The Trojans' defense took over in the second half. After allowing two touchdowns in the first half--as many as the team allowed in its first five games--Gaithersburg limited Churchill (4-2, 4-1) to just 33 yards in the second half.

Colbert carried 23 times last night and was held in check by Churchill's undersized defenders on many of those carries. But he broke off the two long touchdown runs and also had a pair of 26-yard runs in the second half to set up a field goal and a touchdown. He has 2,997 yards rushing in his career and has scored 11 touchdowns this season.

In what might be another school record, the Trojans scored on their first offensive play for the third consecutive game. Colbert, who started last week's 36-0 victory over Magruder with a 74-yard touchdown run, started off tackle, then bounced to the right and made a nifty cut around a defender en route to a 72-yard touchdown.

Later in the half, with Gaithersburg leading 14-6, Tyronne Bailey intercepted a pass in the end zone to give the Trojans possession. Colbert ran for three yards on first down, then turned a run off right tackle into a 77-yard touchdown for a 21-6 lead with 5 minutes 3 seconds left in the half.

"I try every play, ever since I was little, to break it for a touchdown," Colbert said. "Coach Harvill tells me every play isn't a touchdown, but I try to break it anyway."

On both of the long runs, Colbert seemed to slow down as he got to the outside, then sped past defenders as he looked for blockers upfield.

"He has great speed and great moves," Churchill second-year coach Eric Spencer said. "And he has great acceleration out of his cuts. We knew he was a great back and we hoped not to give him any room. When we did, he took advantage of it."

Notes: Churchill fullback Dwayne Douglas did not play because he violated a team rule by having an unexcused absence from class during the week, Spencer said. . . . Churchill quarterback Matt Rubinoff finished 9 of 25 for 152 yards with two touchdowns and two interceptions. . . . Gaithersburg quarterback Ian Hamilton was 8-of-11 passing for 82 yards with one touchdown.

CAPTION: Trojans' Jay Colbert breaks loose for 77-yard TD in second quarter. He finished with 256 yards, a single-game mark.