Bish Cullins, defending national AAU 106-pound boxing champion, decisioned a game Al Martino last night in the Potomac Valley AAU 112-pound open division final at the Washington Coliseum.

In the night's most exciting match, 20-year-old Aaron Caldwell knocked out Don Steinman in the first round.Caldwell of Washington's Latin Connection, won his 16th in 17 bouts in the 139-pound final. All Caldwell's victories have come on knockouts, 12 of them in the first round.

Caldwell came out stalking his much small er opponent with George Foreman-like ferocity and power, causing the referee to give Steinman a standing-eight count five seconds into the bout. Less than one minute later, Steinman received a second eight-count. The referee mercifully stopped the bout on the third eight-count, less than two minutes into the fifth round.

Cullins, a 17-year-old junior at Bladenburgh High School who fights for the Hillcrest Boys Club, upped his record to 51-9 by calmly outboxing the aggressive Martino, who fights for the Ham Athletic Club.

Cullins landed just enough combinations to notch the victory in the rugged bout. Action was so heavy that each fighter finished with a bloody nose and lost his mouthpiece.

Charles Tuttle of Bowie, the area 1979 Golden Gloves champion, upped his mark to 26-3 by taking a decision in the 156-pound class over Ricky Adkins of the Bowie Boys Club. Tuttle, who fights out of Hillcrest Club, will turn pro after the AAUs.

In the heavyweight division, Al Williams of Finley held onto Annandale Boys Club's Pete Hussey enough to make Hussey wonder what dance music was playing. Williams finally was disqualified in the third round after the refree's third warning.

In the novice division, 147-pound whirlwind O'Dell Montgomery pounded on fellow Ham A.C. fighter Dion Prout's chest until the referee stopped the fight midway in the third round.

The next novice fight was even better. George Cupp of Hillcrest counter-punched his way to a close decision over Bruno Robertson of Ham. Cupp started slowly but built momentum until he was in complete control by the frantic third round.

Last night's open division winners earned a trip to the Eastern Regionals next weekend in Norfolk, Va. Winners there travel to the Nationals May 6-12 in Lake Charles, La.