MOSCOW - Disputes between Russia and the United States over funding and lucrative contracts are hampering an international effort to destroy the world's largest chemical weapons arsenal, experts said Wednesday.

With a commitment to destroy 44,000 tons of chemical weapons by 2012, Russia has eagerly courted foreign funding. More than 20 countries - including members of the Group of Eight - have pledged money for the program, which has been beset by shortfalls.

Western countries have spent hundreds of millions of dollars but only a fraction of that money has been channeled through the Russian government with most going directly to contractors - the vast majority of them non-Russian.

Patrick Wakefield, a deputy assistant to the U.S. defense secretary who is responsible for chemical disarmament and threat reduction, alluded to "some problems" between U.S. and Russian officials over the past year.

"The problems have increased costs and delayed schedules," Wakefield told a conference in Moscow on Russia's progress toward meeting its chemical weapons destruction goals. He did not elaborate, but his comments appeared to be a warning to Russian officials to improve cooperation with Western funders.

Viktor Kholstov, a top Russian official responsible for overseeing chemical disarmament, said Western countries had donated just some $217 million so far, about 7 percent of the $3 billion necessary to build destruction facilities.

Paul Walker of the Washington-based Global Green organization said many of the disagreements hampering progress revolved around the choice of contractors awarded lucrative construction projects.

"There have been a variety of issues just this past year about Russians coming in at the 11th hour and demanding that a different contractor get a major contract," Walker said. "They've held up construction for months."

He said the Cooperative Threat Reduction program - the U.S. agency that funds disarmament in Russia - had frozen contracting for construction of a chemical weapons destruction facility in the Ural Mountains town of Shchuchye for up to five months after Russia insisted on its own candidate to build the site's heating plant. The Russians ultimately backed down.

Wakefield said the United States alone has spent some $709 million so far on building the Shchuchye facility and has earmarked just over $1 billion for it.

Russia signed the Chemical Weapons Convention in 1997, pledging to eliminate its arsenal within 10 years. However, it won international agreement to prolong the deadline until 2012 because of a lack of funds.