Barring a miraculous transaction, the Washington Diplomats will "voluntarily terminate" at midnight tonight, becoming the city's second professional soccer franchise to fold in less than a year.

Duncan Hill, the club's general manager and an owner, has until midnight to meet the North American Soccer League's $150,000 performance-bond deadline. Hill and his father Jimmy, the principal owner, have been trying to sell the team for more than a month, but have been unsuccessful.

"It may be that nothing will be announced until Wednesday morning because our efforts to sell the club will go right down to the midnight deadline," Duncan Hill said yesterday.

"If I said I was optimistic and we didn't come through with a buyer, people would be disappointed. And if I said it doesn't look good and we found a buyer, that would sound stupid, too. That's why I don't want to comment any further right now. I don't want to mislead anybody. It's best to say we're working as hard as we can to keep soccer here."

Vince Casey, an NASL spokesman, said yesterday that the league has no plans to extend the Sept. 15 deadline. League Commissioner Phil Woosnam could not be reached for comment. If the Dips fold, they would be the second NASL franchise to fail this season. Atlanta has folded, and Jacksonville, California and Dallas might. The Calgary franchise is expected to be sold today.

With the termination of the Washington franchise, Duncan Hill could try to sell any of the 20 players on the roster. Those not sold would probably go into a special dispersal draft.

The Hills already have dropped their asking price from $3 million to $2 million. But potential buyers reportedly have have been scared away by reports that the Hills lost more than $1 million this season and owe local creditors as much as $700,000, according to sources close to the club.

The last apparent hope to save the team ended last week when a group led by Gordon Bradley, coach of the old Diplomats, couldn't come up with enough money to make a serious offer.

"There seems to be no way to keep this alive (by midnight)," said Bradley, who described himself as "forever the optimist. What we need is a Jack Kent Cooke type. But that person just hasn't materialized. We had people -- some of them neighbors of mine -- who would call me and say, 'I've got $5,000 if it will help keep the team here.' It was good to hear that, but we're talking about several million dollars."

The most attractive potential buyer was Andrew Mellon, of the wealthy Mellon family, who lives near Middleburg, Va. Duncan Hill met with Mellon at least once, but Mellon, who was not available to comment, reportedly became disinterested because of the league's instability.

Jimmy and Duncan Hill moved the Detroit Express to Washington Feb. 28, giving Washington another Diplomat team just four months after Madison Square Garden had folded a more successful team last Dec. 8.

This season, the team averaged 12,106 fans per game -- 12th in the 21-team league -- at RFK Stadium and took in $70,000 per game -- seventh in the league. The team started the season by winning eight of its first 11 games, but finished 15-17 and did not qualify for the 15-team playoff round.

Woosnam said recently there would be no expansion next season, meaning that Washington could get a team only if one of the league's existing teams moves to Washington.

Jacksonville, whose owner, the Lipton Tea Co., has announced it will not sponsor the team next summer, had expressed interest in moving here before Detroit did. But Bradley and other sources say the league would be very reluctant to let an existing franchise move.

The league has been criticized for allowing the Detroit franchise to hurriedly move here, especially since the Hills were in litigation with limited partner Roger Falker, and owed the Pontiac Silverdome $150,000. But many owners and Woosnam have been adamant in maintaining that Washington is one of the four or five best potential soccer markets in the nation.

The Hills were criticized for not taking the advice of knowledgeable soccer enthusiasts in the area and for poor marketing strategy.

"I still think this is a good soccer town," Bradley said. "I can't believe we'll have no sport in Washington next summer. Washington seems to be an affluent town with no big money. It's difficult to expect to sell a soccer franchise in five or six weeks.

"Without being condemning, I think the Hills, more than anyone, realize the mistakes they made in running the franchise for a year. But the price we will now pay for those mistakes is too much for them to learn."