Smith, White and Adams sparked a 20-2 run to build a double-digit lead midway through the second half that put Texas A&M (23-7) in control.
The trio accounted for 35 of the Aggies' first 40 points.
Ashleigh Fontenette scored 21 points for Texas (22-10), but the Longhorns committed 26 turnovers and struggled to score against the Aggies' aggressive defense in the second half.
Fourth-seeded Texas A&M defeated the fifth-seeded Longhorns for the eighth consecutive time, including three meetings this season.
The Aggies last won the Big 12 championship in 2008, the last time the tournament was played in Kansas City. They play undefeated and third-ranked Nebraska on Saturday.
Texas' third-year coach Gail Goestenkors is 0-8 against Texas A&M.
After Fontenette's two free throws gave Texas a 40-38 lead early in the second half, Texas A&M responded with a 20-2 run to build a 16-point lead with 9 minutes left. Smith, White and Adams combined for 13 of the 20 points. Texas went nearly six minutes without a point during the spurt.
Sydney Colson hit a big 3-pointer during the Aggies' run before getting a steal and converting a layup to give Texas A&M a 62-45 lead with 8:07 left.
For 24 minutes stretching from the first half into the second, only Smith, White and Adams scored for the Aggies. They combined to score 29 of Texas A&M's first-half points, including the Aggies' final 27 before halftime.
Smith scored 11 in the first half, while Adams and White added nine apiece.
The three then scored the Aggies' first six points of the second half before Damitria Buchanan made a layup with 14:47 left.
Texas, which had pulled away from 12th-seed Missouri in the final minutes on Thursday, routinely turned the ball over and never appeared comfortable offensively against Texas A&M.
Texas A&M's offense wasn't crisp at times, either.
Adams' layup with 4:45 left in the first half snapped a nearly four-minute scoreless stretch and gave the Aggies a 26-24 lead. Smith then scored four straight points to put Texas A&M in front 30-24.
Texas only trailed 34-30 at the break despite being plagued by turnovers and 39 percent first-half shooting.