Robert Newhouse scored twice in the fourth quarter as the Dallas Cowboys rallied to defeat the winless St. Louis Cardinals, 21-12, at Texas Stadium yesterday.

Tony Dorsett rushed for 154 yards and scored a touchdown.

Newhouse, the Cowboys' robust fullback scored on a two-yard run and a 15-yard pass from Roger Staubach after the Cowboys went into the fourth period trailing, 12-7.

The defending Super Bowl champions have won three of four games, having lost only to the Los Angeles Rams a week ago.

They still trail the undefeated Washington Redskins by one game in the NFC East with a showdown coming next Monday night at RFK Stadium.

The Cowboys lost the ball on fumbles the first two times they had it and St. Louis turned the second into seven points. The touchdown came on a 19-yard pass from Jim Hart to Mel Gray.

On Dallas' fourth play of the game, Roger Staubach passed to tight end Billy Joe DuPree for 27 yards but DuPree fumbled the ball as he was hit by Mike Sensibaugh. Perry Smith picked it up and returned it 42 yards to the Dallas 38.

The Cardinals could get no closer than the 33, however, and punted.

Dallas ran one play the next time before Tony Dorsett was hit by Bob Pollard and fumbled. Sensibaugh picked up the ball and St. Louis took over at the Dallas 44. Eight plays later, Hart threw to Gray and St. Louis was on the scoreboard.

The Cardinals made it 10-0 with 11:36 left in the second quarter on a 23-yard field goal by Jim Bakken.

Dallas finally got something going on its next possession as Staubach moved the Cowboys 71 yards in 12 plays. Dorsett scored on a seven-yard run and Rafael Septien's point after cut the Cardinals' lead to 10-7 with 6:23 left in the half.

St. Louis worked into position for another field goal attempt late in the half, but Bakken was short from 47 yards.

As if the Cowboys didn't have enough trouble trying to move the ball on the stubborn Cardinals, reserve tight end Jay Salsi broke his arm in the first period and will be out indefinitely.

The Cowboy's ineptitude continued in the third period. They couldn't get out of their own territory on their first three possessions and finally had a punt blocked, resulting in a safety and a 12-7 St. Louis lead.

Dallas punter Danny White was standing on his eight-yeard line. The Cardinals' Jim Thaxton burst through and blocked the kick. It rolled into the Dallas end zone with the Cardinals' John Barefield and the Cowboys' Scott Laidlaw giving chase.

Laidlaw as able to knock it away from Barefield and out of the end zone resulting in the safety instead of a St. Louis touchdown.

Following the ensuind Dallas free kick, Bakken tried a 42-yard field goal, but randy Hughes blocked it for Dallas.

Dallas took over at its 27 and drove 73 yards in nine plays to take its first lead of the day, 14-12, with 13:20 left.

Robert Newhouse scored on a two-yard run. The big plays on the drive were a 25-yard run off tackle by Dorsett to move the ball to the St. Louis 34 and a 23-yard Dorsett run on a trap to the 11. Three plays later Newhouse scored and Septien kicked the conversion.