Israel’s tough-talking former foreign minister, Avigdor Lieberman, pleaded not guilty on Sunday to charges of fraud and breach of trust in a criminal case that leaves his political future hanging in the balance.

An outspoken hard-liner and senior political partner of Prime Minister Benjamin Netanyahu, Mr. Lieberman made his plea through a lawyer in a mainly procedural court appearance as his trial opened. He is accused of having promoted Israel’s former ambassador to Belarus for another post after the ambassador provided the foreign minister with classified information about a police investigation into Mr. Lieberman’s financial affairs.

As the trial gets under way, Mr. Netanyahu is engaged in delicate negotiations to form a governing coalition after the January elections in which Mr. Lieberman ran as Mr. Netanyahu’s No. 2 on a rightist ticket.

After the court proceedings on Sunday, one of Mr. Lieberman’s lawyers, Jacob Weinroth, said: “We are very pleased. We’ve passed the preliminaries.”

“We want this to end quickly, and we want it to end well,” he said. The next four court sessions are scheduled for late April and early May.

Mr. Lieberman will not be eligible for a ministerial post unless he is acquitted, but he has indicated that he intends to clear his name and return to the cabinet, preferably as foreign minister. Earlier this month he told Israeli television that the foreign affairs portfolio would remain with Mr. Netanyahu pending the trial’s conclusion.

Mr. Lieberman, an immigrant from the former Soviet Union who rose to prominence as the leader of the ultranationalist Yisrael Beiteinu party, is still serving as a member of Parliament and as temporary chairman of the legislature’s prestigious Foreign Affairs and Defense Committee. But if he is convicted of offenses that include moral turpitude or receives a prison sentence of three months or more, he is likely to be forced to quit political life for several years.

Mr. Lieberman’s critics are asking how Foreign Ministry employees who may be called as witnesses by the prosecution can be expected to testify against Mr. Lieberman, given the possibility that he may return as their boss.

The spectacle of senior public figures on the witness stand has become commonplace in Israel. A former prime minister, Ehud Olmert, was acquitted last year of corruption charges in two major matters but was convicted of breach of trust in a third. He remains embroiled in another corruption case having to do with the construction of a residential complex while he was the mayor of Jerusalem. And Moshe Katsav, a former president, is serving a seven-year prison term after being convicted of rape.

Testimony by the prosecution’s central witness — Danny Ayalon, who served as deputy foreign minister under Mr. Lieberman — is expected to be a highlight of Mr. Lieberman’s trial. Mr. Lieberman removed Mr. Ayalon from the party’s ticket shortly before the elections for reasons that were not publicly specified.

Mr. Lieberman’s defense is thought to rest partly on the argument that he did not intervene to promote the ambassador to Belarus to the same post in Latvia, but that the diplomat was the best candidate for the job.

According to the prosecution, Mr. Lieberman instructed Mr. Ayalon, who led the Foreign Ministry’s Appointments Committee, to advance the appointment of the diplomat to the post in Latvia, and Mr. Ayalon did as he was asked.

Since his unexpected exclusion from the new Parliament, Mr. Ayalon has become critical of Mr. Lieberman and his policies as foreign minister. On Saturday, Mr. Ayalon said in speech at a regional forum that Mr. Lieberman had tried to push through inappropriate diplomatic appointments. Mr. Ayalon said he had resisted those moves, according to the newspaper Haaretz. He also said that Mr. Lieberman had failed to win the trust of foreign governments and should not serve another term as foreign minister.

The journalist Shalom Yerushalmi wrote Sunday in the newspaper Maariv that “anyone who wants to hear the testimony of outgoing Deputy Foreign Minister Danny Ayalon against Lieberman is going to have to order tickets.”

“Ayalon,” he added, “is brimming with revenge.”