In a case that is of political significance to Mayor Dennis J. Kucinich, City Council President George L. Forbes, who heads the political opposition here to the mayor, goes on trial Monday on public corruption charges.

A conviction would require Forbes to forfeit his office. Forbes has led the council in repeated confrontations with Kucinich's administration, including the battle over the Municipal Light plant that led to the city's going into fiscal default last December.

Forbes, five other councilmen and two former legislators were among 18 peiple indicted last October in connection with an alleged City Hall-protected carnival gambling scheme.

Investigations resulted in 498 indictments - the largest number to be brought at one time against public officials in Ohio - charging that the officials accepted bribes in exchange for facilitating city permits for carnivals where police said illegal gaming devices were used.

Forbes was indicted on 14 charges of bribery, theft in office, extortion, intimidating a police officer and engaging in organized crime. The organized-crime charges were dropped when the trial judge ruled they were vague and unconstitutional.

Forbes and his police bodyguard, Curtis Watkins, will be the first to go on trial. The other trials, including those of carnival operators and employees, will start later this summer.

Kucinich is expected to make public corruption an issue in this year's mayoral and council elections. His campaign forces are believed lining up candidates to run against selected councilmen who may be discredited by the coming trials.

If Kucinich can increase his influence in the City Council, he will be more successful in pushing through his policies, which have been at the heart of his confrontations with the council. Kucinich, who was elected in November 1977, has vetoed more than 60 pieces of legislation - and most of his vetoes have been overriden by the 33-member, Forbes-led council.

Forbes, who has been council president since 9173, is the son of a Tennessee cotton-picker. After migrating to the north, Forbes became a lawyer. He had changed in the past 15 years from a dashiki-clad black nationalist who was frequently seen with militants during the urban uprisings of the 1960s to an establishment political leader who is as comfortable with corporation presidents today as he is with ghetto social workers.

Forbes and Kucinich served on the council together and at one time were allies in the political wars against Ralph J. Perk, Kucinich's Republican predecessor.

Whatever friendship existed disappeared after Kucinich's election as mayor, to be replaced by a clash between Forbes' status quo brand of government and Kucinich's so-called urban populism. Their most celebrated clash came over the Municipal Light plant, which Forbes wanted the city to sell and Kucinich wanted it to keep.

The upcoming trials have stirred racial passions in this already polarized city, where whites hold a 60-to-40 percent population edge over blacks. Black political leaders have complained that the trials are an attempt to purge the city's black leadership - a charge denied by county prosecutor John T. Corrigan, who points to his successful prosecutions of several white office holders on corruption charges.

Of the eight present and former councilmen indicted, one, Mary Ann Lecate, is white. The other councilmen under indictment are Lonnie L. Burten, Ceasar Moss, David Collier and John Barnes.