As convicted spy Jonathan Pollard approaches 25 years behind bars, Israelis and others are renewing efforts to secure freedom for the former U.S. Navy intelligence analyst, who is serving a life sentence for relaying military documents to Israel.

Pollard's case has been a source of constant friction between Israel and the United States, its staunchest ally. Israeli leaders have failed to persuade Washington to release the 56-year-old American Jew, whom Israelis and some U.S. officials say was given an unduly long sentence for spying for a friendly government.

Several recent appeals have come from those who consider Pollard's life sentence unjustified.

Lawrence Korb, an assistant secretary of Defense at the time of Pollard's arrest in November 1985, wrote in a public letter to President Obama in late September that the sentence was too harsh and the result of an "almost visceral dislike of Israel" by former Secretary of Defense Caspar Weinberger.

Korb says the average sentence for Pollard's offence is two to four years and under current guidelines the maximum sentence is 10 years.

Rafi Eitan, the former chief of the Israeli intelligence unit that recruited Pollard, last week claimed that the U.S. had reneged on its verbal pledge to release Pollard after 10 years. Eitan said Pollard remained imprisoned despite the fact that some of the U.S. charges against him — specifically, spying for the former Soviet Union — had been refuted.

Eitan said some espionage activities originally attributed to Pollard were later discovered to have been the work of Russian mole Aldrich Ames, who was arrested in 1994.

Pollard's New York-based attorneys last week filed a new petition for clemency, asking Obama to commute the sentence to time served.

Their request was supported by a letter recently circulated by four Democrats in Congress urging Obama to release Pollard as a way of encouraging Israel to take risks for peace.

The issue was even reportedly broached during recent talks aimed at crafting a list of American incentives to persuade Israel to extend its partial freeze on West Bank settlement construction and get peace talks back on track. But officials on both sides later distanced themselves from the proposal.

"Right now, I hope there is some change in the atmosphere," Yuli Edelstein, Israel's diaspora affairs minister and one of several Israeli politicians who have visited Pollard in his prison cell in Butner, North Carolina, said in an interview. "I would dare say that in the last few weeks there is more attention on this issue. But we've already suffered several disappointments in the past."

Edelstein added that there have been high-level discussions among Israeli government officials on ways to obtain Pollard's release.

Nevertheless, obstacles stand in the way of Pollard's freedom. Some analysts say that with the midterm elections near, Obama may be reluctant to enter discussions on the issue with the defense and intelligence establishments, which may fear that a release would suggest U.S. leniency toward convicted spies.

Furthermore, Israeli Prime Minister Benjamin Netanyahu may not wish to push an issue that could stir diplomatic tensions.

Pollard's supporters insist that he acted out of loyalty to Israel. But that argument has been undermined by allegations that Israel provided him with cash, jewelry and expensive travel in return for the documents, and later funded some of his legal fees.

Pollard's wife, Esther, wrote in the Jerusalem Post newspaper on Monday that the statements by Korb and Eitan "provide Israel with the golden key to open Jonathan's jail cell." She also lambasted the behavior of successive Israeli governments toward her husband as "morally bereft" and condemned the Netanyahu government for failing to act to free Pollard.

It was in 1998, during Netanyahu's first premiership, that Israel officially acknowledged that Pollard was one of its spies. Until then, he had been described as part of an operation not sanctioned by the government. When Pollard was on the run from U.S. authorities in 1985 and sought refuge at the Israeli Embassy in Washington, he was denied entry.

Through the years, the Pollard case has come up during diplomatic negotiations and election campaigns.

"Pollard is not different from any other one of our soldiers," said Uri Ariel, a right-wing legislator who leads the parliamentary group lobbying for Pollard's release. "We don't neglect soldiers anywhere, not in this field either."