The most important player in the push for Mideast peace that President Bush launches with a high-stakes conference next week may be one that's not on his long list of invited guests.

For varying reasons, Iran is a force driving the United States, Israel, the Palestinians and their Arab backers to seek a deal now. Many other motives come into play, but the growing influence and uncertain aims of Tehran provide rare unity of purpose among states that are key to solving the six-decade Israeli-Palestinian conflict.

The United States has asked nearly 50 nations and organizations to attend next week's coming-out party for what U.S. diplomats say will be serious, continuing set of negotiations to establish an independent Palestinian state alongside Israel.

Israeli and Palestinian leaders jumped out ahead of their U.S. hosts by committing themselves to such bargaining even before the three-day session in Washington and Annapolis, Md., had begun. The Annapolis conference, as the Bush administration is calling it, now serves largely as a platform for those who could help or hurt the peace effort to have their say.

All those, that is, except Iran.

Long the chief U.S. adversary in a volatile region, Iran stands accused of funding and arming terrorist groups, including Palestinian factions that do not want a peace deal with Israel.

According to U.S. and other Western intelligence, Iran has helped establish what amounts to a client state in the Gaza Strip, the smaller of two Palestinian territories that would make up an eventual independent nation.

Shiite Iran is also a worrisome power for majority-Sunni Arab states such as Saudi Arabia, which have watched with alarm as Iran angles for influence in chaotic Iraq and allegedly seeds Islamic extremists bent on overthrowing secular or U.S.-allied Arab governments.

Israel calls Iran an existential threat and takes seriously Iranian President Mahmoud Ahamadinejad's calls to wipe the Jewish state off the map. Israel says its own intelligence shows Iran is closer than the West has estimated to being able to build a nuclear weapon.

Iran has already pronounced the U.S. sponsored peace session a hopeless exercise, but the clerical regime is sure to watch the meeting closely for clues to U.S. strength and motives in the Middle East.

Secretary of State Condoleezza Rice said it's "a strange argument" to call Iran an organizing principle behind this latest effort to resolve an old conflict, and said the Israeli-Palestinian dispute needs a solution on its own merits.

But, she said, "it is in fact the case that there is a regional context here," in which Arab states are newly motivated to end the conflict.

"Maybe they understand the broader threat of extremism in the region and that extremists use this conflict" to organize and recruit, Rice said Friday as the United States waited for word about which Arab states would attend.

Saudi Arabia's participation is considered crucial, as the most powerful Sunni state that has not made peace with Israel and a longtime U.S. ally. Saudi Arabia is also the author of a dormant Arab peace plan that the Bush administration has partly adopted as a rubric for new negotiations.

Riyadh has not publicly committed but is expected to send an envoy. It is not clear whether that would be the canny and well-respected foreign minister, Prince Saud al-Faisal. Lower-level representation would be an unsubtle sign that the kingdom does not put great weight in the Annapolis effort.

The Bush administration considers the conference a kind of challenge to Arab states to act on their frequent complaints about the Palestinian plight.

The session, the first such peacemaking effort under Bush's banner, is also an implicit answer to criticism from Arabs and elsewhere that the administration has largely ignored the Palestinian problem or has allied itself too closely with Israel.

"This time we've tried to have Arab engagement and involvement all along the way," Rice said, comparing this effort with previous failed attempts. "The Arabs are going to need to support this process and support it fully."

Arab and other Muslim states — including U.S. adversary Syria — make up about half the guests invited to Annapolis.