The base to be built in Brdy, 55 miles southwest of the capital, Prague, is part of a U.S. missile defense system that Washington wants to install, with 10 missile interceptors in Poland, purportedly to counter a threat from Iran and other "rogue" states.
The activists, Jan Tamas and Jan Bednar, who began their hunger strike on May 13 in central Prague, demand that the Czech-U.S. talks on the base end and that a nationwide referendum be held on the issue.
Jan Bednar was earlier briefly hospitalized with liver problems but has vowed to continue his strike.
"We have tried almost everything, but our government has failed to listen to us," Tamas said on his Web site. "This is no longer only about the radar base or international security. It is about democracy. We fear for our country's democracy."
The government of the Czech Republic approved the U.S. plans on May 21. The basic document still needs to be ratified by the country's parliament and signed by President Vaclav Klaus.
An opinion poll conducted in April showed that two-thirds of Czechs were against the U.S. missile shield plans.
There is also considerable opposition to the deployment plan in the Czech parliament, with the leading opposition force, the Social Democratic Party, demanding public dialogue on the issue.
Russia has fiercely opposed the plans, saying the Central European shield would destroy the strategic balance of forces and threaten Russia's national interests.
