David O. (Sonny) Werblin, chief executive officer for Madison Square Garden, said last night that he is beading a group that has "just about agreed to terms" for the purchase of the Washington Diplomats soccer club.

If the Werblin group consummates the sale, it likely will move the Diplomats to New York.

Werblin Previously has said he would like to put a soccer team in Shea Stadium, where the football Jets and baseball Mets play. But he was reluctant to go into detail last night because he wants to handle negotiations on a cautious basis until "the papers are signed."

"We are in discussion with the Diplomats," the onetime operating head of the Jets aid, "relative to a purchase of the club, but a deal has not been concluded. It will be subject to (North American Soccer) league approval."

Werblin, apparently influenced by the immense success of the Cosmos in Giants Stadium in East Rumbertard, N.J., reportedly wants to have a team in a market of 20 million people. His group would have to indemnify the Cosmos, who have territorial rights.

Stephen I. Danzansky, president of the Diplomats, said yesterday that he had talked to Werblin about selling the club but remarked, "Nothing has been sold."

Danzansky did say that he has been investigating the sales potential of the Diplomats and would make a recommendation on whether to keep or dispose of the team at a meting of the board of directors in New York City the first week in October.

Danzansky also said that there would be no stipulation that a buyer would have to keep the club in Washington.

Danzansky said that Werblin was one of the 15 persons be talked to about sellinng the Diplomats and that a list of prospective buyer had been narrowed to 10 before Werblin came into the picture.

Asked why the club was considering selling out. Danzansky said: "How long can you lose money?"

He noted that the stock of SJR Communications, which owns the Diplomats, is traded on the New York Stock Exchange and that "our first responsibility is to produce profits."

There was a report in July that the Diplomats faced a loss of $500,000 for the second straight year. Danzansky would not specify amounts but said the club has had "significant losses" each year since SJR took over in 1974.

He pointed out that the team had been improving its position to the extent that "at first it was costing us $6 to make $1, then four,,then three. Soccer is the obvious sport of the future; it is here to stay."

He remarked that "Washington is the eight-largest market in the country demographically and by television standards. If our board decides to sell, we would have to get a price equal to that market value.

"If somebody does buy, the price would be based on the value of a NASL franchise, the value of the players' contracts. And the territorial rights in Washington are worth more than in, say, Memphis or Tulsa."

He mentioned that when expansion franchies were awarded in 1977 to Memphis, Detroit. Houston and Denver, the price was $1 million each, with half of the money being required immediately and the rest coming from future revenue.

Danzansky said that those new teams would not share a television revenue and money from possible other expansions until franchise costs were paid off.

He noted that, in contrast. "The Washington franchise has been operating since 1974 and is a good territory with an established audience."