The Diplomats are back.

Ninety-six days after professional soccer in Washington was left for dead by Madison Square Garden Corp., the owners of the Detroit Express were granted permission yesterday by the North American Soccer League to move their team here for the 1981 season and rename it the Diplomats.

After three days of back-room wrangling, league owners unanimously approved the franchise move yesterday during a conference call overseen by league Commissioner Phil Woosnam.

Express General Partner Duncan Hill, who has been in Washington the last four days negotiating with potential investors and the league ownership, said he will sign a five-year lease with no escape clause with the D.C. Armory Board. The new Diplomats will open their home season in RFK Stadium against the Montreal Manic -- formerly the Philadelphia Fury -- on Saturday, April 11.

"We feel, as does the league membership, that Washington is an excellent soccer city," Hill said. "That was proven by the Diplomats last year. We don't expect to draw the way they did because that was the result of months of planning and an excellent marketing effort. We've only got six weeks until opening day, so we can't expect those kinds of results.

Basically, we feel as if we're now a year behind where the Diplomats were before Madison Square Garden folded the team. If we could average about 15,000 this year, I would be delighted. I would hope the next year that we would do as well as the Dips would have this year if they hadn't folded."

Hill also said that he had committed the new Dips to playing in the NASL indoor league next winter. The old Diplomats never played indoors, except for a disastrous series of exhibition games in the D.C. Armory during the winter of 1978.

The only remaining barrier to the move -- and it is not considered major -- is a motion filed last night in Detroit to block the transer by Harold Van Arnem, a limited partner (4 percent) in the Express. Van Arnem sued the team a year ago when the other partners demoted him from general to limited partner. He is seeking an injunction in federal court against the franchise shift because that litigation is still pending. Judge Horace Gilmore will rule on the motion Monday morning.

Average attendance for the Dips was 19,205 last season, with much of the credit for that figure going to Joh Cruyff's presence. Hill said it was unlikely the team would attempt to re-acquire the Dutch midfielder now playing in Spain. "If I had to choose between spending money on one John Cruyff or four or five other talented players, I would take the four or five players," he said. "I think we need to build this club with young players, improve it year by year."

The Express was 14-18 last year and did not make the playoffs. The team will play in the Eastern Division this year under the league's new five-division setup. The Cosmos, Montreal and Toronto also are in the division. The Cosmos will play here twice, May 23 and June 17.

The move also means that Paul Cannell, one of the most popular players in Washington soccer history, will be returning here. Cannell was traded to Memphis after the 1979 season following a dispute with the Dip's management, then to Detroit during the winter. He will be a starting striker for the new Dips.

Hill said he will look into the possibility of acquiring members of the original Dips, many of whom left Washington grudgingly. The Express had a working agreement with Coventry City of the English league's First Division. That is the first team Alan Green, the Diplomats' all-time leading scorer, played for professionally.Green is currently under contract to the Jacksonville Tea Men.

Hill said one of his first priorities is to determine the role of former Diplomat Coach Gordon Bradley with the team. Ken Furphy, coach of the Express throughout its three-year existence, will remain as coach. Bradley is expected to be involved in marketing and personnel.

The Express cam here because its attendance held steady at about 11,000 during its three years in Detroit because of the depressed economic situation there, and because of the large, well-organized youth soccer programs in this area.

Some NASL owners objected to the move because the season starts on March 28, four weeks from today. With Woosnam pushing hard because he badly wants a team here, the owners quickly voted for the move during the conference call.

The NASL will consist of 21 teams this season, down from 24. Since the end of last season, Washington, Houston and Rochester have folded. Detroit has moved to Washington, Philadelphia to Montreal and New England to Jacksonville.