NEW YORK, OCT. 7 -- Bess Myerson, the former Miss America whose political charm helped Edward I. Koch win election as mayor, was indicted today on charges that she illegally influenced a state judge to reduce alimony required to be paid by Myerson's lover.

Myerson, 63, who served as Koch's cultural affairs commissioner until she was forced to resign in April, hired the judge's daughter as a $19,000-a-year aide in exchange for having the divorce case fixed, according to the six-count indictment returned by a federal grand jury here.

Myerson's millionaire boyfriend, Carl A. (Andy) Capasso, 45, a city sewer contractor who began serving a four-year prison term for tax evasion last spring, is also charged in the case, as is Hortense W. Gabel, 74, who recently stepped down as a Manhattan Supreme Court judge.

If convicted, Myerson could face up to 30 years in prison and $513,000 in fines. The three defendants are charged with mail fraud, conspiracy and bribery-related charges. Myerson is also charged with obstruction of justice.

Myerson "unequivocally asserts her innocence of all of the charges . . . . At long last, she welcomes the opportunity to confront the charges against her," her lawyer, Frederick P. Hafetz, said.

Gabel said she is "innocent of any wrongdoing" and that "there has never been the slightest question of my integrity."

For Myerson, who lost a race for the Senate in 1980 and who has long been one of New York's most popular figures, the charges illuminate a seamier side of her life known here as "the Bess Mess."

The indictment said Myerson used fictitious names when phoning Gabel, visited her during weekends on Long Island and entertained the judge's daughter, Sukhreet, at Capasso's Westhampton Beach estate.

Myerson, whom Capasso's ex-wife, Nancy, blamed for breaking up her marriage, was described as receiving a "substantial" amount of "money, jewelry, vacations {and} furnishings" from Carl Capasso, along with the use of his chauffered limousines and credit cards.

This latest chapter in the city's widening corruption scandal has also been the most difficult for Koch, a longtime Myerson friend criticized for not following up the original allegations in 1983.

The indictment charged that Myerson deceived Koch, other city officials and the news media, made "false and misleading statements" and later tried to prevent Sukhreet Gabel from giving honest testimony to the grand jury.

Koch, who has since declared an end to his friendship with Myerson, told reporters today that her "ethical behavior was absolutely wrong, disgraceful."

U.S. Attorney Rudolph W. Giuliani, calling the affair "a very sad case," said the city had paid Sukhreet Gabel's salary "in essence as part of a bribe." He also questioned why courts did not seek misconduct charges against the judge in 1983.

"When you are sitting on a case where the correspondent in a matrimonial matter employs your daughter, that is a matter that should cry out for investigation," Giuliani said.

The indictment said Myerson and Capasso, her "steady and intimate companion," conspired with Gabel, who had been pressing city and state officials to find a job for her daughter, then 34, to fix the Capasso divorce case.

Myerson became cultural affairs chief in April 1983. That July, soon after Gabel had introduced her daughter to Myerson, the judge halved the $1,500 a week personal support and $500 a week child support that she had ordered Capasso to pay his ex-wife.

A month later, after having an aide help Sukhreet Gabel prepare her resume, Myerson hired Gabel as her special assistant. Myerson later took the judge, her husband and Sukhreet Gabel to dinner to celebrate the hiring and charged the bill on Carl Capasso's credit card.

Capasso pleaded guilty in January to evading $774,000 in taxes by falsifying expense accounts.

Myerson, who in 1945 became the only Jewish Miss America, told New York magazine last March: "The reason this is happening is that I'm a woman. I'm a Miss America . . . . I'm Queen of the Jews . . . . I'm a commissioner. I'm the perfect route to the downfall of this administration."

Myerson, who got her political start as consumer affairs chief under Mayor John V. Lindsay, campaigned tirelessly for Koch, then a little-known member of Congress, in the 1977 mayoral race.