Reserve tailback Howard (Beaver) Petty ran 23 times for 121 yards and scored four touchdowns yesterday as his White team beat the Orange team, 42-7, in Virginia's annual spring football game in Charlottesville.

Petty, a 197-pounder who was redshirted last season because he had mononucleosis, scored twice from the two, once from the seven and once from the 22.

Three of his touchdowns came in the first half as the White took a 28-0 lead behind the quarterbacking of Mike Eck, who completed 10 of 15 passes for 63 yards.

Eck had a three-yard scoring run for the White's final touchdown before intermission.

"We've known all along that Petty is a fine back, and since he had to sit out last season, we've got him for four more years," Coach George Welsh said. "I've said all along that we have some pretty good talent at running back and at the skill positions . . . "

Doug Porter, the backup quarterback on the White team, passed to wide receiver Quentin Walker for a five-yard touchdown in the third quarter.

The Orange touchdown came on a 31-yard pass from senior quarterback Wayne Schuchts, the starter for most of the 1982 season, to split end Billy Smith in the fourth period. Schuchts was eight of 16 for 118 yards.

White fullback Derek Jenkins ran 16 times for 87 yards and flanker Nick Merrick caught three passes for 71 yards. Smith finished with three catches for 103 yards for the White . . .

In Annapolis, sophomore quarterback Sean Cannon completed seven of eight passes, one for a touchdown, as Navy's Gold defeated the Blue squad, 10-0, in the annual scrimmage that ends spring practice.

Cannon threw a seven-yard pass to tight end Mark Stevens midway in the third quarter for the game's only touchdown.

Second quarterback Adam Meinrod, another sophomore, started the touchdown drive with a 38-yard pass to Eric Wallace. Meinrod completed seven of 10 passes for 105 yards.

Sophomore Todd Solomon kicked a 48-yard field goal for the other points.

Stevens caught five passes for 88 yards.