Marwan Barghouti, the popular imprisoned Palestinian leader, embodies the promise and the peril Israel faces as it negotiates with Hamas to trade hundreds of Palestinian prisoners for a long-held Israeli soldier.

Islamist Hamas says Mr. Barghouti tops the list of approximately 1,000 prisoners it is demanding Israel free in exchange for Sgt. Gilad Shalit, who Hamas has held captive in Gaza for more than three years.

Senior Israeli and Hamas officials said late last month the two sides were close to a final deal. But since then, Hamas officials have told Arabic media that Israel objected to a handful of prisoners on their list and insisted on deporting many freed prisoners abroad, causing a delay. Hamas officials now say they think a deal is possible by month's end.

Israeli Prime Minister Benjamin Netanyahu is under intense pressure to win Sgt. Shalit's freedom. But giving in to Hamas demands to free top Palestinian leaders and militants carries significant political and, some say, security risks.

The highest-profile name on Hamas's list, and a likely sticking point, is Mr. Barghouti, a leader of Palestine's Fatah faction. His supporters compare him with South Africa's Nelson Mandela, who at various stages in the fight against apartheid advocated peaceful coexistence and armed resistance. To his critics in Israel, he is a terrorist, serving six life sentences in prison for a 2004 conviction on five counts of murder in relation to attacks on Israelis.

"Barghouti is one of the many prisoners who, if they are included in the deal, it will hand a great victory to terror," said Israeli technology minister Daniel Herschkowitz, who, as a cabinet member, will be required to approve any prisoner release. "On the other hand, the state has an obligation to stand behind its soldiers."

Mr. Barghouti's release could have a far-reaching impact on domestic Palestinian politics and the peace process. The Fatah leader could help heal the rift between his secular party, which holds sway over the West Bank, and Hamas, which has effective control of the Gaza Strip.

Palestinian opinion polls show Mr. Barghouti is capable of handily defeating current Palestinian president Mahmoud Abbas, who represents the old guard of Fatah, and is also more popular than any likely Hamas candidate. His popularity also could provide impetus for a Palestinian-wide vote, which has been delayed in part by the rift between Hamas and Fatah.

Some Israelis and Palestinians believe the secular, Hebrew-speaking Mr. Barghouti is among the few Palestinian leaders who could effectively engage with Israel in any serious peace deal, and have the political legitimacy to sell the deal to Palestinians. From his jail cell, Mr. Barghouti helped broker a cease-fire with Israel in 2003 and spearheaded an effort to reconcile the warring Fatah and Hamas factions in 2006.

Mr. Barghouti touches a raw nerve in Israel, however. Though he supports a negotiated two-state solution, he continues to advocate the right of Palestinians to resist Israel's occupation, by force if necessary. He condemns targeting civilians inside Israel proper, a position that implicitly supports attacks on Jewish settlers and soldiers in the West Bank.

The 46-year-old Mr. Barghouti was born in the West Bank and emerged as a young activist leader in Yasser Arafat's Fatah in the late 1970s and 1980s. He became fluent in Hebrew during four years in Israeli prison beginning in the late 1970s and was exiled abroad for his role in the first Palestinian intifada, or uprising, in 1987. In 1994, he returned to the West Bank after the signing of the Oslo Peace Accords and was elected to the Palestinian parliament.

During the latter half of the 1990s, he worked closely with Israelis. "He was an educator and very cooperative partner working with us to build a new reality between the young people of both societies," recalls Janet Aviad, an Israeli peace activist.

But Mr. Barghouti also represents many Israelis' sense of betrayal and disillusionment after peace efforts in 2000 failed, and Palestinians turned to violence in what became known as the second intifada.

Mr. Barghouti emerged as the uprising's most visible leader. He urged Palestinians to take up arms and led protests and marches that often ended in clashes with Israeli forces.

In 2002, Israel arrested Mr. Barghouti and charged him with 26 counts of murder, convicting him on five counts two years later. He has denied the Israeli accusations.