It will cost any new owner of the Washington Diplomats $500,000 to keep Johan Cruyff's contract from reverting back to the Cosmos on Dec. 1, according to sources in the current Washington organization.

Cruyff initially signed a North American Soccer League contract with the Cosmos two years ago. Those rights were sold to the Los Angeles Aztecs in May 1979 with payment deferred. That debt was passed on to the Diplomats, along with Cruyff, last February.

Since Madison Square Garden Corp. has decided to give up on the team, it will not make the payment due the Cosmos Nov. 30. If new owners for the team can be found between now and Nov. 23, the last day that MSG could fold the franchise, they will have to decide within seven days whether they want to retain their rights to Cruyff.

Last season it cost the Garden about $1.2 million to have Cruyff in a Diplomat uniform. About half covered the purchase price from Los Angeles; the rest covered salary. Totaling the payment owed the Cosmos and whatever salary would be negotiated with Cruyff, the cost would be about the same next season.

Diplomat President Steve Danzansky, who is trying to put together a group to buy the team before MSG folds it, said yesterday a decision to keep Cruyff probably would be the first thing any new owners would have to discuss.

"It would all depend on the group and just how much money was available," Danzansky said. "There are some who think it a necessity for Johan to remain, others in this town who don't think he's worth the price tag. I think if it could be worked out I would like to see him return."

Right now, though, Danzansky is more concerned about saving the franchise. "Time is so short it's difficult," he said. "When San Juan Racing decided to sell out two years ago I knew about it in July and had more time to find a buyer. Now though, we're scrambling."

Madison Square Garden posted a bond to operate the team 1981 on Oct. 24. It has 30 days from that date to "voluntarily terminate," by turning its certificate of ownership to NASL Commissioner Phil Woosnam. Because of that deadline, a buyer must be found by Nov. 23. MSG Chairman Sonny Werblin had made it clear he will fold the team if a buyer cannot be found.

Woosnam has been trying to help Danzansky by talking to prospective investors about the league. The situation should be clearer this weekend when owners meet in Chicago to discuss a number of matters, including what Woosnam now has labeled "the Washington situation."

Danzansky, who has first refusal rights on any sale, said he would willingly step aside if he cannot put together a group and another potential buyer came along who would keep the team in Washington.

"I've nursed this baby six years," he said. "All I want now is someone who will raise it right. If it's someone else, that's fine, as long as they make a real commitment to the team and the city."