A gamble by nonplaying captain Bob Kelleher paid off yesterday as the United States Davis Cup team took a 2-0 lead over Great Britain in the Interzone finals in Bournemouth, England.

America's top player, Chuck McKinley, blasted Mike Hangster, 7-5 to give the U.S. a 1-0 lead, and Frank Froehling, named a starter by Kelleher only 24 hours before play began, outstroked lefthander Billy Knight, 4-6, 6-5, 6-4, 6-4.

The U.S. team needs only to win today's doubles match or one of the two singles matches Saturday to defeat Britain. A win this weekend and a victory over a weak India team would set the U.S. in the challenge round for the first time in three years.

But the U.S. might not have gotten past Great Britain if Kelleher's gamble had misfired. No Davis Cup captain is supposed to field anyone except his two top-ranking players in Cup play. National honor is at stake, and all that. So everyone assumed that McKinley and Dennis Ralston, who had carried the U.S. past Mexico in the American Zone finals, would play.

But Kelleher decided otherwise. Ralston had been brilliant against Mexico, whipping Rafael Osuna to win for the U.S. after Osuna had beaten McKinley.

Afterwards, however, Ralston's game seemed to slump. He lost sets to several unheard-of players in the U.S. championships, then was defeated in the quarterfinals by Brasil's Ronnie Barnes. Froehling murdered Barnes the next day, giving him seven games in three sets.

Froehling went on to the finals and impressed everyone before losing to Osuna. But one tournament does not make a tennis player, and Froehling had looked simply awful earlier this year. Apparently Kelleher decided to gamble with Froehling's hot hand and his experience on the kind of clay courts used at Bournemouth, rather than Ralston's erratic tennis. The gamble now seems to have paid off handsomely.

But down in Australia, the world's reigning tennis champions are preparing an ambush for the invading Americans. Roy Emerson, no long stale, and Ken Fletcher, no longer inexperienced, are backed up by Fred Stolle, whose flame-thrower serve took him to the Wimbledon final against McKinley In addition, there is talk of reactivating Neale Fraser, whose canny court sense helped Australia hold the Davis Cup for five years Fraser is still only 29, and he held every major tennis title at some time before retiring early last year.

Erratic U.S. Team

But if the U.S. team loses, the primary cause will be the U.S. team itself. McKinley is a reliable player, but after him the team is as inconsistent as a racquet with broken strings. If they play well, the Aussies may not win a match, and if they play poorly, not even Bob Kelleher's intuition can save the Americans It's even possible, though most unlikely, that they could lose the match with England. With this team, not even the certain is certain.