Having defeated Czechoslavakia, 4-1, in the Davis Cup quarterfinals, the United States now is strongly favored to beat its next opponent, Australia, Oct. 2-4 in Portland, Ore.

"Australia has potential, but I think we should be favored against anyone," said John McEnroe, whose rout with Tomas Smid assured the American victory today.

Both McEnroe and Jimmy Connors said today that they will be available to play against Australia.

"I'll keep coming back to play Davis Cup as long as they want me," McEnroe said.

"I would like to help the team win the cup back," said Connors, who played Davis Cup for the first time in five years here. "That would be important to me."

Arthur Ashe, the United States Davis cup captain trying to avoid alienting any of the numerous top American players at his disposal, hedged when asked whom he would choose for the Australian series. But he can be expected to name McEnroe and Connors, two of the three top-ranked players in the world, to compete in singles.

In doubles, Ashe most likely will choose between McEnroe-Peter Fleming, the two-time Wimbledon champions and top-ranked team in the world, and the veteran team of Bob Lutz and Stan Smith.

Ashe decided to save McEnroe for singles against Czechoslavakia in New York's summer heat, but the semifinals will be played indoors in Portland and the U.S. captain admitted he "would be less resistant to using McEnroe in singles and doubles."

But Ashe might follow his successful format against Czechoslavakia and go with Smith-Lutz, who have a 113-1 lifetime Davis Cup record.

"Right now, Smith and Lutz have an edge on everybody," said Ashe, possibly trying to patch up a misunderstanding with the pair over Ashe's original choice of Gene and Sandy Mayer for the Czech series. Smith and Lutz joined the team only when Gene Mayer hurt his wrist at the French Open last month. "They're playing well," Ashe said. "They made the Wimbledon finals and won their match here (9-7, 6-3, 6-2 over Ivan Lendl and Smid)."

Australia advanced to the Davis Cup semis by defeating Sweden, playing without Bjorn Borg, this weekend in Sweden. Borg chose to rest after Wimbledon.

The Aussies' greatest strength is their doubles team as Peter McNamara and Paul McNamee, but doubles accounts for only one of the five matches in Davis Cup competition. McNamara-McNamee lost to Smith-Lutz in five sets in the Wimbledon semifinals 10 days ago, but won the tournament in 1980.

Incredibly, McNamara-McNamee lost to Swedes Per Hjertquist and Stafan Simonsson, both 21, in five sets Saturday.

"How McNamara and McNamee managed to lose to Sweden, I don't know," said Ashe. "That just underscores what I said a few days ago about crazy things happening in the Davis Cup."

Ashe said he didn't know who will play singles for Australia in October. The Aussies used McNamara and McNamee, ranked 15th and 33rd in the world in singles (as of June 15), in Sweden on clay, but could change their lineup on a faster indoor surface. Other candidates are Kim Warwick, ranked 25th; Phil Dent, 48th; Mark Edmondson, who upset Roscoe Tanner to win a Wimbledon tuneup tournament in June, or possibly Wimbledon semifinalist Rod Frawley.

Should the United States defeat Australia, the Americans would most likely play Argentina in the finals on clay in Argentina. That should prove a severe challenge. Argentina beat the U.S., 4-1, the last time they met in the Davis Cup in 1980. In that series, McEnroe, who is not confident on clay, lost to Guillermo Vilas and Jose-Luis Clerc.