Three key players, including middle linebacker Ed Simonini of the Baltimore Colts and two regulars from opponents in the Redskins' NFC East Division, incurred major injuries in a full Saturday night of NFL preseason play. The night's action was highlighted by Los Angeles quarterback Pat Haden's strong performance in a 33-21 victory over Dallas.

Simonini broke his clavicle in the Colts' 20-17 loss to the New York Giants at East Rutherford, N.J. Team officials said he would be out indefinitely.

Also lost was Dallas free safety Randy Hughes, who dislocated the same shoulder on which surgery was performed twice last season, in the final minutes of the Rams-Cowboys game. Philadelphia fullback Leroy Harris, who broke two bones in his left forearm in the Eagles' 36-20 victory over the Pittsburgh Steelers, underwent surgery yesterday and reportedly will be out for the season.

In other preseason games Saturday night, Green Bay, which defeated Dallas a week ago, made it two straight with a 34-14 win over defending Super Bowl champion Oakland; Cleveland defeated Buffalo, 13-10; Atlanta beat the New York Jets, 21-20; New England edged Tampa Bay, 17-16; Miami defeated Denver, 24-14; New Orleans won its second straight, 27-7 over Houston; Kansas City beat Chicago, 13-0; San Diego defeated San Francisco, 31-28, and Cincinnati beat Detroit, 30-20.

At Anaheim, Haden straightened out once he stopped trying to be another long passer like Vince Ferragamo, who left the Rams for the Canadian Football League during the offseason.

Haden tried passing long in the team's preseason opener last Monday night and the results were disastrous. Haden was intercepted four times in the first half as the Rams lost, 34-21, to New England.

Saturday, Haden did what he does best, going to a short- and medium-passing game. He completed 17 of 25 passes for 207 yards and was intercepted just once in the first three quarters.

"I tried to forget about last week," Haden said, "but people just wouldn't let me."

Haden's passing helped set up touchdown runs of one and three yards by Wendell Tyler, one yard by Jewerl Thomas and two yards by Mike Guman. Haden threw a four-yard touchdown pass to tight end Henry Childs for the final Los Angeles score.

"I thought Pat Haden threw the ball extremely well tonight and he also made some excellent calls," said Los Angeles Coach Ray Malavasi.

Haden led the Rams in rushing with 38 yards on two scrambles.

The Cowboys (0-2) fell behind, 21-0, after 18:32 of play. The Dallas touchdowns were scored by James Jones on a 30-yard run in the second quarter, Tony Dorsett on a 33-yard pass from Danny White in the third period, and Billy Joe DuPree on a one-yard pass from backup quarterback Glenn Carano with 6:43 remaining in the game.

White, who played a little more than half the game, completed 12 of 23 passes for 156 yards. He was intercepted twice. Jones led all rushers with 68 yards on nine carries.

"We have a great deal of improving to do in all aspects of our game before the start of the regular season (against the Redskins) in three weeks," said Dallas Coach Tom Landry.