Wimbledon champion Bjorn Borg yesterday signed a three-year contract with the Cleveland-Pittsburgh Nets of World Team Tennis (WTT) for in excess of $1 million, confirmed that he will play in the $100,000 Volvo Classic in Washington next month, and said he was unperturbed by the prospect of being sued by a man who is even richer than he is, Dallas oil tycoon and sports entrepreneur Lamar Hunt.

It was a busy day for the 20-year-old Swede. After breakfast in Little Rock, Ark., where he beat Henry Bunis in the first round of a tournament Tuesday night, he flew to New York, Cleveland, and Pittsburgh for WTT press conferences in all three cities. Then he returned to Little Rock, where scheduled to play Anand Amritraj in a second-round match tonight.

While Borg was holding hands with Marianna Siminnescu, his Romanian fiancee, at the Manhattan signing of a package deal for them to play for the Nets this season, Hunt and Mike Davies, executive director of World Championship Tennis, were holding meetings with their attorneys at WCT corporate headquarters in Dallas.

Hunt and Davies claim they were jilted by Borg after getting "a 100 per cent firm commitment" from his agents that he would compete in the $2.4 million "World Series of Tenns," the circuit of 12 tournaments leading to the WCT Finals for the top eight singles players at Dallas in May.

WCT announced last October that Borg, who won the WCT title and Wimbledon last year and is generally ranked No. 2 in the world behind U.S. Open champ Jimmy Connors, would participate in its series. The announcement was authorized by Borg's agents, International Merchandizing Corp. of Cleveland, but no contract was signed, and Borg says he changed his mind about playing WCT in December.

Instead he is plaping the rival Grand Prix tournament series, which formerly ran from May through November, but now goes year-round and clashes with WCT the first four months of the year.

The Volvo tournament at George Washington University's Smith Center, March 14-20, is part of the Grand Prix. Borg's participation is expected to be announced at a press conference today, but he acknowledge by phone yesterday that he has entered.

Borg has been pressured to play the Grand Prix rather than WCT by Bancroft Sporting Goods, which pays him a fee, said to be in six figures, to play with and endorse its rackets in the U.S. Bancroft is a subsidiary of Colgate-Palmotive, which took over sponsorship of the Grand Prix this year.

Ironically, signing with World Team Tennis for its April-through-August season will keep Borg from playing Grand Prix events most of the summer, but he said Bancroft and Colgate were in favor of the deal "because I will be playing mostly in the United States, and that is where they sell rackets."

Borg has a contract with another manufacturer, Donnay, to play with its rackets overseas.

The Washington Post learned that WCT is seriously considering filing litigation against Borg, possible as early as next week.

"We're looking at all the alternatives. We anticipate taking some legal action," WCT director Hunt told the Post yesterday. He said he was "very, very disturbed" by what he considers Borg's reneging on a commitment made on his behalf by his designated agents.

"It's a very important thing to WCT, and to the whole structure of tennis - the question of whether there will be integity in keeping Commitments," Hunt said.

"Lamar and I were in meetings all morning with out lawyers," said Davies. "They have been looking at files, memos, notes, letters, Compiling all the evidence. When they're finished, we'll decide what action we plan to take and will hopefully have a statement Thursday afternoon ir Friday."

Davies said that WCT's integrity is being impugned because he told tournament directors. TV representatives and sponsors that Borg would be playing, based on the word of Bud Stanner, the International Merchandizing vice president who handles most Borg's affairs.

Borg and Stanner both told The Post yesterday that they thought WCT had no basis for a suit because no contracts were signed for Borg's participation in WCT.

"It's unfortunate that this happened," Stanner said. "When Mike Davies asked me if he could use Borg's name at a press conference in October, I told him to go ahead because I thought we were close to deal we had been negotiating for three months. Mike, Bjorn and I all thought we had a deal. But Bjorn changed his mind.

"Mike is just naive if he thinks he wasn't taking a chance making the announcement before contracts were signed," added Stanner." . . . You can call what we did hard dealing, but it isn't illegal."

"I've played WCT for three years, I wanted to do something different . . . For sure, I never made a commitment. If they want to sue me, that's up to them, but I didn't sign nothing," said Borg.

He indicated that the deal for him and the 20-year-old Simionescu to play World Team Tennis was worth more than $1.5 million. He said that a contract for his coach, Swedish Davis Cup captain Lennart Bergelin, was never part of the package engineered by Nets owner Joe Zingale and financed with the help of other owners in the 10-team league.

Borg said that Wimbledon and pissibly one grass court tune-up before hand would be the only European tournaments he will play this summer, but that his WTT contract allows him to play Davis Cup for Sweden if the team can win the first two series without him.