After several minutes of Buddha-like concentration, Tony Sims, 18, attacked a 319-pound barbell yesterday and hoisted it briskly over his head to win the middleweight championship in the Montgomery County Open weightlifting meet in Rockville.

"It was no problem," said the jubilant senior from Theodore Roosevelt high school in Washington. That lift, part of the clean-and-jerk competition, coupled with Sim's snatch lift (a one-motion effort) of 259 pounds, was more than enough to overcome his closest competitor, Bill Bader of Belleville, N.J.

Sim's victory was a major step toward a berth in the Junior World Games this summer in Hungary. Sims, a member of the Crush Unlimited Weightlifting Club of Washington, would be the second black weightlifter to qualify for those games.

Ron Crawley of Crush Unlimited, the first black to make the Junior World Games, won the 123-pound division title yesterday. Crawley snatched 192 pounds and had a personal high of 253 pounds in the clean and jerk.

Crawley's second lift was a struggle. He swayed back and forth before finally managing to get the bar over his head and holding it there.

"It seemed like forever to get the bar over my head," said Crawley, the 1978 teen-age national champion.

Crawley and Sims are shooting for the 1980 Olympics in Moscow. Both helped their cause at this meet as the U.S. Olympic weightlifting manager, Dick Smith, was on hand.

"Both guys showed a lot of fire," said Smith. "That's what it takes to get to the Olympics. It's a certain intestinal fortitude that they both possess. The whole thing was been very encouraging."

Also watching was Marty Schnorf, Junior World Games coach, who said Sims "is definitely a leading contender to go on to Hungary." Sims barely missed qualifying for last year's team that went to Greece.

Crawley, part of that team, has since turned 20 and is no longer eligible. He placed 12th among 32 competitors in Greece.

One competitor in the Montreal Olympics, Mark Cameron of Hyattsville, won the heavyweight division title late last night. Cameron failed in his bid to establish an American record of 375 pounds in the snatch, lifting 352.