As he paraded around the lobby of the courthouse where this city's celebrated carnival kickback trial was concluding last week, City Council Majority Leader Basil M. Russo had the air of a poker player who has just drawn an inside straight.

And, as far as the political bookies here are concerned, he had.

Russo, 31, a three-term councilman, is one of the several candidates running this year againt Mayor Dennis J. Kucinich. He had bet the mayor's race as well as his etire political future that Council President George Forbes would beat the 11 public corruption charges against him.

Russo publicly defended Forbes. This hurt him on the white west side, where Forbes is regarded as a black devil, but had harvested support in the predominantly black east side.

Russo figured that if Forbes was acquitted he could repair the west side damage. But if not, Russo would be linked to a corrput politican and his candidacy would have followed Sky-lab.

The cards fell perfectly for Russo as Cmmon Pleas Court Judge George A. Tyack, in a directed vedict Wednesday afther the prosecution's case, found Forbes innocent of all 11 charges of extortion, bribery, theft in office and intimidating a police officer.

Tyack said the evidence was circumstantial and unworthy of jury consideration. Thursday, the jury acquitted Forbes' police boyguard, Curtis Watkins, of similar charges.

But nothing is engraved in stone in the wilds of Cleveland politics, where alliances can shift as fast as the weather and support often goes to the highest bidder.

For example, there was a time when Forbes and Russo were such bitter enemies that Forbes refused to shake Russo's hand during a televised debate. About that same time, Forbes and Kucinich, who was then a councilman, were close allies.

Other mayoral candidates, attracted to the race by Kucinich's sagging performance in the polls, could snatch away the black support from Russo. Two other notable politicians in the race, so far, are Edward F. Feighan, a Democrat who collected 65 percent of the black vote in his 3,000-vote loss to Kucinich in 1977, and Republican Lt. Gov. George V. Voinovich, a Slovenian with strong credentials in Cleveland's ethnic community.

But initial reaction to the Forbes ruling is that Russo is the chief beneficiary and that Kucinich is the loser.

Forbes' acquittal "will solidify the black vote behind Russo," said Timothy Hagan, chairman of the Cuyahoga County Democratic Party, though that statement was made before Feighan, Hagan's choice for mayor, announced his candidacy Friday.

For Russo, the acquittal gives him the opportunity to continue forging a rare Italian alliance in a city where, only a decade ago, the two groups were spilling blood in the streets over integration.

Russo's game plan is to put together a coalition of blacks, Italians (who represent only 8 percent of the population), and anti-Kucinich liberals to topple the mayor.

Forbes apparently will remain council president, and will continue his iron-fisted rule of the 33-member legislative body, keeping it unified agaist Kucinich.

With Forbes at the helm of the council, it will be difficult for Kucinich to get legislative approval of his programs and policies, especially a plan to repay #14 million to the six banks holding defaulted city loan notes.

Kucinich's aides say default is a political liability for the mayor.

Also, Forbes can help Russo raise campaign funds from the business community, which is anxious to see Kucinich defeated. Forbes apparently has access to the corporate tills, as business leaders chipped in some $100,000 for the defense fund for Forbes and other indicted councilmen.

The black vote had been crucial to Kucinich in the 1977 mayoral election as well as the August 1978 recall attempt against him.

Republican Party County Chairman Robert E. Hughes said that while blacks are riled up over what they perceive as the political persecution of Forbes and other indicted council-men, he questions whether the feeling will last until election day.

An influential black newspaper publisher, W.O. Walker, said he has no such doubts.

"The Forbes verdict galvanized black people into the tighest political unity that we've had for a long time, since Carl Stokes' first administration," Walker said.

Stokes was the first black mayor of a major U.S. city. He was mayor from 1967 to 1971.

Walker said that most blacks believe that Kucinich, who is in charge of the police department, pushed the police investigation on the carnival kickback case as a means of knocking Forbes out of power.

Kucinich has not commented publicly on the case in recent months, though he has in the past called councilmen crooks, Andrew M. Juniewicz, Kucinich's news secretary, said the mayor will maintain his silence. CAPTION: Picture 1, MAYOR DENNIS J. KUCINICH. . . black vote had been crucial; Picture 2, GEORGE L. FORBES. . . gut card in an inside straight