Tusk told journalists in Warsaw before leaving for the 45th Munich Conference on Security Policy that the controversial missile shield - opposed by Russia as a threat to its national security - would be one of the main topics he would discuss with Biden.
"We are a very honest partner of the United States, and if we agree something with the Americans we always keep our word," he said at a news briefing. "We are ready to participate in this project, but the decision, of course, is with the American side."
Moscow has strongly opposed U.S. plans to deploy 10 interceptor missiles in Poland and a radar in the Czech Republic by 2013 as a threat to its security and nuclear deterrent. Washington says the defenses are needed to deter possible strikes from "rogue states" such as Iran.
President Dmitry Medvedev threatened in November to retaliate if the plans go ahead by deploying Iskander-M missiles in the country's westernmost exclave of Kaliningrad, which borders NATO members Poland and Lithuania.
Russian Deputy Prime Minister Sergei Ivanov told the Munich conference on Friday that Moscow would not deploy Iskander missile systems in the Kaliningrad Region if Washington gave up its missile shield plans.
Medvedev "from the very start said clearly" that if "there are no interceptors in Poland and the Czech Republic ... there will be no Iskanders in Kaliningrad," he said.
Top Russian officials have repeatedly expressed hopes that President Barrack Obama will step back from deploying the system, which the George W. Bush administration worked hard to get agreement on with Poland and the Czech Republic.