Mike Thomas' attorney said yesterday he will demand the Washington Redskins trade or release his client, and that he is contemplating an antitrust suit attacking the National Football League's free-agent system.

"We have not negotiated at all about a contract for Mike since last July," Dallas attorney John Dickens said. "What are they trying to do to Mike, kill him?

"I just cannot figure out why they can pay a John Riggins $300,000, a Billy Kilmer $250,000 and not pay Mike."

Dickens said the Redskins gave Thomas, a five-year veteran running back, a "qualifying offer" of $90,000 so they would have the right to match any offer he received from another club.

"That is $20,000 less than what he played for last year, and under no circumstance will I allow Mike to sign a contract for that amount," Dickens said.

"Mike Thomas is not asking for that much. It's in the range of $700,000 to $800,000 over five years, and that's nothing compared to what some of his teammates and other people around the league are getting."

Thomas played ot his option in the 1978 season and has until April 15 to shop around the NFL for a better offer. If he does get an offer from another team, the Redskins would have the right to match it and retain Thomas, or allow him to leave and accept draft choices from his new team as compensation.

If Thomas gets no other offers-so far Dickens says he has none-he would remain in limbo until June 1. By that date, the Redskins must notify Thomas whether or not they want to retain the rights to him.

If they do, Thomas has the option of taking a 10 percent raise (to $121,000) for the 1979 season, or signing the last best written offer from the club.

If the Redskins tell Thomas they do not want him back, he becomes a totally fee agent, and the Redskins would receive no draft-choice compensation should he sign with another team.

Dickens said he would allow Thomas to take a 10 percent increase over his 1978 salary, but that "it would have to be done under a multiyear contract, not a one-shot deal.

"But at this point, I', going to insist that they trade Mike, or release him. I have spoken with Bobby Beathard (the Redskin general manager) and he told me they had tried to trade Mike to 27 other clubs with- out any interest at all, I cannot believe that. You can't tell me for a minute they can't trade Mike Thomas."

Dickens said Thomas has spoken to a half-dozen teams, including Tampa Bay, "but we haven't heard a word from them. That's why I think this whole free-agent system is such a sham.

"There are no free agents going anywhere; it's a joke. There may very well be collusion among the owners, and we are seriously contemplating going to federal court and filing an antitrust suit."

Thomas said yesterday that he is "shocked by this whole thing, that it's gone this far. Evidently they don't want me to play for them, and if they don't want me. I don't want to be there. I want out if it's going to be like this."

Beathard was out of town scouting yesterday and not available for comment. But Redskin Coach Jack Pardee wondered out loud, "Odes Mike have a team for us to trade him to? We'll listen to anyone.

"They (Thomas and Dickens) have made the rounds and talked to teams and we've had teams call us, but nothing is close to being finalized. He's a free agent, he's got choices.

"We have made our plans either with him or without him. We haven't counted Mike in or counted Mike out.

"I think now, more than anything, the players are finding out their value. A lot of times they think they are worth more than they really are.

"I have not been involved in the negotiations, so I don't know what Mike's contract demands are. But when you weigh what the demands are over what the production has been ..."

Pardee did not finish the sentence.

Thomas, who gained more than 2,900 yards his first three seasons and is now second on the Redskins' all-time rushing list, missed three games last year with a controversail foot injury and rushed for only 534 yards.

The controversy developed when Thomas refused to take injections that would have allowed him to play. Several teammates and coaches made it known they thought Thomas could have played , and should have.

"As a coach, there's no way I'll practice medicine," Pardee said. "But, yes, it did hurt us when Mike didn't play; it set back the running game.

"Last year, some phases of the game were good for Mike and others weren't-his playing time. He didn't play full time; he was more int he specialist category. It just wasn't a good year running."

"I thought I had a better year than the way they are putting it," Thomas said. "Am I angry? No, this is the off-season, time to relax. I even go out there (to Redskin Park) and lift weights. I'm healthy, my foot's fine.

"I just want to play. If it's not here, well, I can deal with that. Definitely."