Rep. Richard Kelly (R-Fla.) yesterday became the sixth congressman to be indicted by federal grand juries in the Abscam undercover operation.

Kelly, who immediately issued a statement denying any criminal conduct, was indicted here yesterday along with two other persons who also allegedly participated in a conspiracy to trade Kelly's congressional influence for bribes from FBI undercover agents.

According to the criminal charges filed against the three men, Kelly took $25,000 of a promised $250,000 from the FBI undercover agents in return for promising to introduce a bill to help an undercover agent posing as a foreign businessman.

Kelly has admitted taking the money, but said he did it because he was conducting his own undercover operation for some "shady characters" trying to buy immigration legislation for wealthy Arab clients.

Kelly is the second congressman to be indicted in Washington for his Abscam role. Rep. John W. Jenrette Jr. (D-S.C.) was indicted here about one month ago and is scheduled for trial in September.

Four congressmen -- Frank Thompson Jr. (D-N.J.), John M. Murphy (D-N.Y.), Michael O. Myers (D-Pa.) and Raymond F. Lederer D-Pa.) -- were indicted earlier in Brooklyn.

Allegations of misconduct against Sen. Harrison A. Williams Jr. (D-N.J.) are still under investigation, as are possible charges against Rep. John P. Murtha (D-Pa.). Murtha was named as an unindicted co-conspirator in one earlier indictment.

Kelly said yesterday in a prepared statement that he viewed the indictment against him as a "grossly cynical manipulation of the criminal justice system for political ends." The only Republican caught up in the Abscam investigation, he noted that the criminal charges were filed "as the Republican convention opens, and little more than six weeks" before his primary election in Florida.

Kelly is "confident he will be found innocent" and is "eager for the current allegation to come to trial so a record of the truth will be laid before the public . . .," the statement said.

Indicted along with Kelly were Stanley Weisz, a New York accountant, and Eugene Ciuzio, a business consultant in Florida and an acquaintance of Kelly's there.

A fourth person in the alleged plot, William Rosenberg of Lynnbrook, N.Y., pleaded guilty last week to one count of conspiring to bribe Kelly. He is expected to testify against the congressman.

According to the charges filed yesterday, the four men agreed to divide $250,000 in promised payments from the FBI agents posing as Arabs. Kelly was scheduled to receive $100,000 of that amount and the three other men were to get $50,000 each, the charges said.

The plot began last November when Weisz and Ciuzio first met and discussed paying a congressman in exchange for immigration assistance for foreign businessmen, according to the charges. Weisz then later told Rosenberg that he found a congressman -- Kelly -- who would accept the money, the charges continued.

Kelly actually met with the undercover agents and accepted the money on Jan. 8, according to court records. The payoff took place at a Washington house rented by the undercover agents and was videotaped, sources have said.

Kelly had said he kept the money in his car's glove compartment and returned it to the FBI the day after the Abscam operation became public. He replaced about $174 of it that he had spent, he said.

All three men indicted yesterday were charged with conspiracy to commit bribery and defraud the United States of the proper services of a congressman. Kelly was also charged with receiving a bribe, and all three men were charged with violating racketeering statutes that prohibit crossing state lines to commit illegal acts.