Dallas Cowboys running back Tony Dorsett and quarterback Danny White decided yesterday to cross their striking teammates' picket line to prepare to play on Sunday, and several other prominent National Football League players announced they will, too.

St. Louis receiver Roy Green and defensive end Curtis Greer declared they will cross the Cardinals' picket line and return. The Cardinals will play the Washington Redskins at RFK Stadium Sunday.

Fifteen defectors in all returned to their clubs yesterday, making a total of 39, on 15 various teams, who actually have given up the walkout.

Another handful of players, including San Francisco 49ers quarterback Joe Montana and teammate Dwight Clark, said they will decide soon whether they will return to work. Others, including Denver Broncos quarterback John Elway, said they will not picket and have not ruled out breaking from the NFL Players Association strikers' ranks.

The Cardinals, Cowboys, New Orleans Saints and Pittsburgh Steelers -- and those clubs' opponents Sunday -- appear to be the teams that could be affected most by veterans deciding to return to action.

White, not a big union supporter to begin with, said he found it difficult to "look in the mirror" and justify being out when his contract calls for him to make $725,000 this season. He resigned from the union.

Dorsett said that, after Cowboys management told him he stood to lose an annuity and some land that had been included in his contract, he had no choice but to return. And veteran defensive end Ed (Too Tall) Jones, who also received an ultimatum from Cowboys management, said he will return.

Four of the Saints crossed the picket line, including nose tackle Tony Elliott, receiver Eric Martin and defensive end Bruce Clark. Pittsburgh veteran center Mike Webster and 1,000-yard rusher Earnest Jackson walked out of a meeting with union chief Gene Upshaw and joined the Steelers' replacement team. John Stallworth and Calvin Sweeney also walked out during the middle of that meeting but didn't announce whether they would rejoin the team by Friday morning at 9 o'clock. That is the NFL-imposed deadline for striking players to rejoin their teams and be eligible to play this weekend.

Upshaw, the NFLPA's executive director, insisted that the union's solidarity will not be affected by the defections. He returned to Washington after his latest flying visit to a strike city and said players, with the help of local labor union employes, will have picket lines at every stadium on Sunday and Monday night.

Upshaw said, "We have more guys out than they have in."

When it was pointed out that several of the returning players are among the most recognizable in the NFL, Upshaw said, "What you have to look at are the guys who are out. I don't think three or four guys in the National Football League constitute the will of the players. Any player that goes in is actually helping management bust the union . . . We are not about to fall for the tactic of trying to divide the players."

So far, the number of union players who have chosen to cross the picket lines since the strike began Sept. 22 is less than 3 percent of the membership. Leaders for both the NFLPA and the NFL Management Council said no negotiations have been scheduled. The owners still say they will not return to the bargaining table until the union changes its position on free agency, the primary obstacle to a new collective bargaining agreement.

Upshaw said, "We are not taking any issues off of the table." John Jones, spokesman for the Management Council, said the owners "are not about to" change the current, restrictive free agency system.

Asked about players who cross the picket lines for any reason, Upshaw said, "Players have a way of dealing with those types of situations. I'm not a player anymore. I'm not threatening anyone and I don't intend to threaten anyone. We're not advocating violence. But sometimes crazy things happen and we'll just have to wait and see."

Some owners and even a few agents said that, by Sunday, they expect more than 100 players will have returned to active duty.

Webster, Jackson and safety Kelvin Middleton told the Pittsburgh Post-Gazette they intend to be ready for Sunday's game against the Atlanta Falcons. "I'm not ready to turn over control of my career to Jack Donlan {the owners' chief negotiator} or Gene Upshaw," Webster said. "That's what I've decided to do at this point. The main thing is I've decided to make the decision for myself."

Danny White, who has had well-publicized financial problems, is saddled by several recent business deals that went bad, said, "I decided to come back in on Monday when I heard Gene Upshaw say the union was in it for the long haul. I realized then he was not representing me . . . The financial situation I'm in and some clauses in my contract were a factor."

Dorsett, one of the most vocal union supporters, earlier this week had called defensive lineman Randy White "Captain Scab" when he crossed the picket line. Dorsett said then he would never have any respect for any player who crossed.

But Dorsett told teammates on the picket line yesterday that he had little choice after receiving a letter from Cowboys President Tex Schramm that indicated Dorsett stood to lose a portion of his annuity, in addition to some land also promised him in his contract.

Schramm confirmed sending the letter (and another letter to Jones), but wouldn't go into details other than, "It involves a lot of money."

Dorsett, who also has had severe financial problems, said, "My mind was made up for me. I have no choice."

Danny White said he felt it was difficult for him to lead the team on-field after not supporting the 1982 strike and realized there may be a similar reaction even though he is in support of the union this time, but opposed to a strike. "I have a hard time looking myself in the mirror when I'm making $725,000 and go on strike like I'm being treated unfairly. Other players feel they have been mistreated, but I just can't convince myself."

Cowboys player representative Doug Cosbie said he understood why White and Dorsett, who are losing in excess of $40,000 per week, had to return.

The Cowboys play the New York Jets in the New Jersey Meadowlands Sunday, and one demonstration will be outside Giants Stadium. Striking Jets and Giants will play tag football in a parking lot. George Martin, the Giants' player representative, said fans will be invited to join in.

"I think it will be a better brand of football than what's being played inside," Martin said.

Denver's Elway, who recently became the league's highest-paid player, said he will not picket. "As good as Mr. {team owner Pat} Bowlen is to us, I don't think we need to be walking in front of his office. Everybody knows we're on strike anyway. You could drag me out there, and I still wouldn't be on the line."

Asked if he will return to work, Elway said, "It depends . . ."

The San Francisco Examiner reported that as many as ten 49ers, including Montana and Clark, were considering coming back. Clark told reporters, "I'd like to say I went out with all the guys and I'm going to stay out with all the guys, but it's not that simple."