At 5-foot-4 and 110 pounds, Tracey Austin hardly looks like an irresistible force, but she has played tennis like one in reaching the final of the $250,000 Colgate Series Championships.

Last night of the 18-year-old high school senior from Rolling Hills, Calif., defeated weary Wendy Turnbull, 6-2, 6-1, in 56 minutes at Capital Centre.

Austin will not a chance to avenge last year's loss in the final here to Navratilova, however, because 15-year-old Andrea Jaeger upset the expatriot Czech, 6-4, 4-6, 6-1, in the second semifinal.

That sets up a Monday night final between these two teenagers for the $75,000 first prize. The tournament takes a sabbatical today, in deference to the National Football League conference championship games.

Austin was overwhelmed by Navratilova in the final of this elite, eight-woman playoff last year, and would dearly like to make amends. Her form has been devastating so far. She has lost only nine games in three matches, beating Virginia Ruzici, 6-0, 6-3; Hana Mandlikova, 6-3, 6-0, and Turnbull, who wilted after three games.

The speedy 28-year-old Australian, who lost to Austin in all five of their 1980 matches, came on court looking resolute and determined to be patient. She played a strong game to hold serve for 1-1, hitting two forehand winners and an overhead, then jerking Austin out of position with a solid forehand down-the-line that opened up the court for an easy volley.

But her first hurrah was also her last. Austin held serve at love for a 2-1 lead, having put all 10 of her first serves in court to that point, then broke Turnbull on her way to a four-game streak. Turnbull was never in the match thereafter.

The first point of the 1-2 game was significant. Turnbull sliced a good first serve wide to the forehand, an ace against most players, but Austin lunged, caught up with the ball practically on top of the courtside press table and groped her return deep. Turnbull surprised, hit a forehand beyond the baseline.

Austin had delivered her calling card. She looked especially eager, alert, and intense. There seemed to be an extra bounce in the dance she does while getting ready to return serve. Early on Turnbull got the idea that this wasn't going to be her night.

Turnbull lost serve at 15 in that game, netting two weak backhands and pushing a forehand long. Thereafter she grew increasingly ragged, and resignation replaced the early keenness in her eyes.

The effort of upsetting Mandliikova in three sets, then teaming with Rosemary Casals to win the doubles title over Candy Reynolds and Paula Smith in a third-set tie breaker Friday evening, had taken its toll. She had an energy crisis.

"I started to get tired in the third set of the doubles. It was a real long and tension-packed match. I got weary then, and didn't sleep well," Turnbull said. "I like to serve and volley against Tracy, but she gets such good depth on her groundstrokes, it's difficult. I just didn't have any sort of fighting spirit out there. I couldn't seem to get up for the match."

Turnbull likes to follow second serves to the net on fast-carpet surfaces, and did so successfully against Mandlikova, but she had too much respect for Austin's returns to do so last night. Instead, she stayed back and rallied, but that was unwise. Austin made only a handful of unforced errors, and Turnbull lost nearly every baseline rally. She was under constant pressure.

Turnbull slices her backhand, never hitting with topspin, and she never got enought weight of shot to trouble Austin, who played to that side. Turnbull did try to throw in some of the drop shots that she disguises well off that side, but Austin covered most of them and hit deep, forcing shots off them.

"I think she generally plays the backhand of most players, and I don't have a backhand that can hurt her," said Turnbull, a realist. "Once she broke me in the first set . . ." Her voice trailed off, then she added: "I had a really tought match against Hana last night, the doubles was a cliffhanger, and that took a lot out of me. I knew I had to be super-fit and keen against Tracy, and I just didn't have it out there today."

Austin just kept rapping her Grim Reaper groundstrokes, and getting to practically every ball. This night, she wasn't even extended enought to do much squealing. She was sharp, quick, and on the ball -- practically flawless from the backcourt, and not too shabby at the net the times Turnbull drew her in.