By Ramin Mostafavi

TEHRAN (Reuters) - Iran's supreme leader rejected the Palestinians' U.N. statehood bid on Saturday, saying any deal that accepted the existence of Israel would leave a "cancerous tumor" forever threatening the security of the Middle East.

As leader of a country under a long-standing threat of military action from Israel and the United States, Ayatollah Ali Khamenei warned the Jewish state and its allies to expect "paralyzing blows" that a NATO missile shield could not prevent.

"Any plan that seeks to divide Palestine is totally rejected," Khamenei told a conference on the Palestinian issue.

"The two-state scheme, which has been clad in the self-righteousness of the acceptance of the Palestinian government and membership at the United Nations, is nothing but a capitulation to the demands of the Zionists or the recognition of the Zionist regime on Palestinian land," he declared.

Israel's U.S. ally has vowed to veto the Palestinian request for full U.N. membership, now being discussed by a U.N. Security Council panel, if it goes to a vote.

Khamenei's speech underlined Iran's support for groups that oppose Israel, including Hamas, the Islamist faction which rules the Gaza Strip and which rejected the U.N. bid presented by President Mahmoud Abbas as "begging" for statehood.

The 72-year-old cleric also sought to portray Iran as the greatest defender of the Palestinian cause, criticizing other countries in the region that have close ties to Washington. Two of these, Egypt and Jordan, have recognized Israel.

"Governments that host Zionist embassies or economic bureaus cannot advocate support for Palestine," he said in comments aimed, among others, at post-Mubarak Egypt with which Tehran is seeking to restore the diplomatic ties cut since 1979.

While Washington seeks to accelerate a return to Israel-Palestinian talks in order to avoid a vote on statehood, Khamenei mocked Barack Obama's support for Israel as a cynical ploy to retain the U.S. presidency at next year's election.

"In order to remain in power you have surrendered to humiliation and to the Zionists," he said.

Iran is pursuing a nuclear program that the United States and Israel say aims to produce atomic bombs, a charge it denies.

Both countries say they do not rule out pre-emptive strikes on Iran to stop it getting the bomb. Tehran says it would hit back at Israel and U.S. interests in the region and analysts say it could use allies, such as Lebanese Hezbollah, to retaliate.

"The West must either give up its bullying policies and recognize the Palestinians' rights and avoid pursuing the Zionist regime's bullying schemes. Otherwise it will face harsher blows in the near future," Khamenei said.

He said a NATO early-warning radar system being deployed to protect the Western alliance from attacks by countries including Iran would be ineffective.

"What threatens the Zionist regime is not Iran's missiles or the resistance, under the pretext of which they have set up the missile shield in the region.

"The main threat comes from the determination of those who no longer want America, Europe or their lackeys to rule over them. Of course (our) missiles will carry out their duties any time they feel a threat stemming from the enemy."

(Additional reporting by Hashem Kalantari; Writing by Robin Pomeroy; Editing by Alistair Lyon)