By Sarah Morland and Daphne Psaledakis

(Reuters) -A top U.S. official in Haiti said on Wednesday that continued U.S. funding for the U.N.-backed security force in Haiti would not be guaranteed if the Security Council rejects Washington's proposal to restructure and expand the mission.

"The U.S. provision of support for the MSS (Multinational Security Support mission) and what we have been providing will expire at the end of December," U.S. charge d'affaires in Haiti Henry Wooster told reporters, when asked if Washington will continue to provide support if the plan is rejected.

Wooster said, however, that he was cautious of speculating on future funding decisions.

The Kenya-led MSS deployed in Haiti in June last year but has struggled to make headway in curbing violent armed gangs - some of which Washington has designated as terrorist organizations - in and beyond the capital of Port-au-Prince.

The mission, built by voluntary contributions from member states, has struggled with a lack of funds, troops and equipment such as armored vehicles. Around 1,000 troops have deployed, short of a target of some 2,500.

The new model proposed by the U.S., which would rename the MSS as the Gang Suppression Force and restructure its leadership, aims to deploy some 5,500 troops, although this is also set to be provided by voluntary contributions.

"We need more numbers," Kenya President William Ruto told Reuters in an interview on Wednesday. "We need more logistics, we need more equipment, and we need more financial support to be able to carry this through."

Ruto told the United Nations General Assembly in New York that Kenya had stepped up in the belief that the mission would be a genuinely multinational effort, but the world had not shown up for Haiti and the mission lacked the logistical support that would accompany other U.N.-sanctioned missions.

U.N. data on Wednesday showed that a trust fund set up for the original mission had received $113 million, more than half from Canada, with the U.S. in second place at $15 million. It was estimated to cost hundreds of millions to run each year.

The mission's current mandate will expire on October 2.

(Reporting by Daphne Psaledakis in Washington, Doyinsola Oladipo in New York and Sarah Morland in Mexico City; Editing by Mark Porter and Edmund Klamann)