JERUSALEM — With its president facing up to 16 years in jail for rape, Israel was transfixed yesterday by the sleazy details of the most serious constitutional crisis in the 58-year history of the Jewish state.

Faced by a revolt from MPs protesting at his behavior in office, President Katsav opted out of opening the winter session of parliament, normally one of his most important ceremonial roles.

Instead the 60-year-old head of state, a married man with five children and six grandchildren, stayed at home in his official residence in the upmarket Rehavia suburb of west Jerusalem, planning his next move.

While Mr. Katsav’s fate rested in the hands of the Israeli attorney general, who must decide whether to charge him, the presidency issued a defiant statement denying any wrongdoing and claiming that Mr. Katsav was the victim of a plot.

With Israeli legal experts describing the charges as the most serious ever faced by an Israeli leader, the case has raised question marks about the future of the state presidency. The crisis came just as a group of opposition members of parliament declared their support for a plan to do away with a purely ceremonial presidency and replace it with a directly elected, American-style position.

Whatever the constitutional fallout, one thing is certain: The gray, bland reputation enjoyed by Mr. Katsav has been blown away by the lurid details of the allegations. According to graphic accounts carried by the Israeli press, the head of state is alleged to have behaved like a sexual predator, groping, manhandling, and ultimately raping two women, including his office manager, at the residency.

The plaintiff, known as Witness A, told police investigators, “When we were in his office, he attacked me with such cruelty, he removed my pants by force from the back and raped me.”

When she tried to complain, he allegedly threatened to have her fired. “I’m the president and you’re nothing,” he is alleged to have said. When she eventually went to the police, it is alleged that a mysterious, unidentified man came to her family home and said, “The president will shut up if ‘she’ shuts up.”

Mr. Katsav’s defense team is believed to have denied this version of events on the grounds that his office, where the alleged rape took place, had glass walls. They said he would never have tried anything in a place open to public view.

When the original accusations surfaced this summer, police sources hinted Mr. Katsav was being investigated for the relatively mild offense of sexual harassment. But when investigators from a specially formed police unit started their work, they said they found a pattern of behavior that went far beyond sexual harassment.

Ten women were interviewed by the police, who concluded that Mr. Katsav raped not just Witness A but another woman who worked for him in the late 1990s.

Her account was printed by the Yediot Achronot newspaper. “It began with compliments,” she said. “Then it continued with a paternal hug. A little while later the hug became stronger. It got to the point of groping, touching my body, my hair, my legs. There were times he asked me to come to his office with a skirt or a button-down shirt that is easy to take off. I asked him several times to stop, but it didn’t help. His reaction was to exploit my position until I was forced to leave the office.”

Under Israeli law, rape carries a jail sentence of between three and 16 years, but the police also said there was evidence to support charges of indecent acts by force, indecent acts without consent, and sexual harassment.

Another tranche of nonsexual offenses were uncovered by police, including fraud, arising from Mr. Katsav’s alleged use of presidential funds to buy private gifts, and illegal phone-tapping to keep tabs on what his staff were talking about.