DENVER, JAN. 9 -- What once was lost was found again as Debi Thomas recovered her U.S. Figure Skating Championship women's title tonight. The national diadem belonged to Thomas alone, with only minor interference in the free skating competition at McNichols Arena from defending champion Jill Trenary and Caryn Kadavy.

Trenary received the silver medal, Kadavy the bronze.

Thomas, skating to music from Bizet's "Carmen" with some help from Mikhail Baryshnikov and the American Ballet Theatre, drew assorted scores of 5.8 and 5.9 out of a possible 6.0 from the nine judges. The end of her balletic four-minute program was greeted with a hail of flowers from the crowd of 15,869, to whom it was immediately obvious that she had won back the title she lost last year and is going to the Calgary Olympics next month as the best U.S. hope for gold. Bedlam was followed by obligatory tears on the medal stand.

". . . When they played the Olympic March, I lost it," she said. "It hit me all of a sudden how much I accomplished."

Thomas' 1987 loss to Trenary had been considered an aberration. Thomas had come into the '87 event suffering tendinitis in her ankles and inconsistent training while in pre-medical studies at Stanford University. But tonight she was healthy and in superb form, having briefly enlisted Baryshnikov and ABT choreographer George de la Pena to help with her operatic theme.

"Last year was kind of strange for me," she said. "It never really hit me that I lost the title."

Its return seemed entirely fitting, despite a clean, elegant program by Trenary to Tchaikovsky in which she landed five of six triple jumps to garner scores ranging from 5.7 to 5.9.

Kadavy's performance was less impressive, a Spanish theme that was marred by her bad fall on the second triple jump of the routine. But she recovered to post predominantly 5.7s and 5.8s.

Thomas' title was a clear signal that she has returned to the form she needs to challenge reigning world and Olympic champion Katarina Witt of East Germany in Calgary next month. In addition to her national title, Thomas lost her 1986 world championship to Witt in Cincinnati last spring, still afflicted with the tendinitis that also deprived her of the U.S. title.

Tonight, she opened with a rare triple-triple combination, an unusual feat for a woman skater. Although she skated conservatively for the rest of the routine and displayed an occasional misstep, she landed four triple jumps cleanly and that was more than enough to win.

"I got kind of tired at the end," she said after electing to do a double in place of one of her anticipated triple combinations. "I told myself, whatever you do, just stand up."

The medalists in the women's division represented the last of the Olympians to be named at this competition, after a grueling two days of events made more difficult than necessary by ill-conceived scheduling on the part of local organizers. The men's division finally concluded at 1 a.m. today when Brian Boitano claimed his fourth straight gold medal, and the late hour drew a storm of protest from coaches and competitors.

"It was so bad that I don't think this will ever happen again," said Boitano's coach, Linda Leaver. "They put the athlete last, and that shouldn't be."

Under the circumstances, some stumbles by world pairs bronze medalists Jill Watson and Peter Oppegard were understandable as they repeated as U.S. champions. They returned to McNichols early today for the long programs after competing in the short programs well into Friday night, and getting just five hours sleep.

Watson and Oppegard, expected to challenge Soviet dominance of this event in Calgary, collected an array of marks from 5.7 to 5.9 for their routine to "Madame Butterfly." That was despite a fall by Watson on a throw triple lutz, and leaving out another jump combination entirely. They made up for the slips with spectacular original choreography including a death drop that entails her free-falling headfirst almost to the ice before he catches her.

Gillian Wachsman and Todd Waggoner won the silver medal for the second year with a correct but uninspired Spanish motif that received scores ranging from 5.6 to 5.8. The lone surprise was in third place, as Wayne and Natalie Seybold made the Olympic team to the "William Tell Overture" and edged out defending bronze medalists Katy Keeley and Joe Mero.