* Trip to follow immediately power transfer deal signing
* Yemen leader requests U.N. assistance after deal - Ban (Adds quotes, background)
By Patrick Worsnip
UNITED NATIONS, Nov 23 (Reuters) - Yemeni President Ali Abdullah Saleh has told U.N. chief Ban Ki-moon he will come to New York for medical treatment immediately after signing a deal that would ease him out of power, Ban said on Wednesday.
The U.N. secretary-general told reporters the Yemeni leader told him of the trip during a telephone conversation on Tuesday. Saleh arrived in Saudi Arabia on Wednesday and, according to a live television broadcast, signed the deal brokered by Gulf states.
"He told me that he will come to New York to take medical treatment immediately after signing this agreement," Ban said.
This is the fourth attempt to wrap up a power transfer deal that Saleh has backed out of on three previous occasions at the last minute.
Saleh was previously forced to seek treatment in Saudi Arabia for injuries suffered in an apparent assassination attempt in June after the last time he ducked out of the deal, which ushered in street battles that devastated parts of the Yemeni capital Sanaa.
"If he (Saleh) comes to New York, I'll be happy to meet him," Ban said.
Under the Gulf Cooperation Council deal, which U.N. envoy Jamal Benomar helped to negotiate, Saleh is to shift all powers to his deputy, Abd-Rabbu Mansour Hadi, who would form a new government with the opposition and call an early presidential election within three months.
Saleh would keep his title until a successor is elected.
Ban said Saleh had asked him that the United Nations should provide "necessary support" after the signing of the deal.
"I told him that the United Nations will spare no efforts and ... I will do my best to mobilize the necessary resources and support so that peace and stability and democratic order will be restored in Yemen," the U.N. chief said.
"He told me clearly that he will hand over all powers," he added.
Ban said he hoped the United Nations would be able to "be present and continue to monitor and help the full implementation of this agreement." He gave no further details, but in other countries the U.N. has helped organize elections.
Envoy Benomar is due to report back to the U.N. Security Council next Monday on his mission to Yemen. (Editing by Anthony Boadle)