WARSAW, July 7 (Reuters) - Polish Foreign Minister Radoslaw Sikorski flew to Washington on Monday to try to salvage talks with the United States on missile defence after Warsaw rejected a U.S. proposal to upgrade Poland's armed forces.

The United States wants to base 10 missile interceptors in NATO ally Poland as part of a drive to counter perceived threats from what Washington calls "rogue states", particularly Iran.

But Poland has sought in return billions of dollars in U.S. investment to upgrade its air defences, including Patriot ground-to-air missiles. Last Friday, the government spurned a U.S. offer as insufficient but said it was open to more talks.

"I think we've got a signal from the American side that they are ready to negotiate," Polish Foreign Ministry spokesman Piotr Paszkowski told TVN 24, adding that Sikorski expected to hold talks on Monday with U.S. Secretary of State Condoleezza Rice.

"Today's meeting (of Rice and Sikorski) is the most important. Any possible discussions (on missile defence) would take place as a result of this meeting," he said.

Rice is scheduled to visit Prague on Tuesday to sign a treaty to build a tracking radar on Czech soil as part of the missile defence plan. The treaty has still to be ratified by the Czech parliament where it faces some opposition.

If she and Sikorski manage to clinch a deal on the Polish interceptors, Rice would likely visit Warsaw at the end of her European trip, probably on Thursday, diplomats say.

"We are preparing for the visit (of Rice) as if it were to take place," Paszkowski said.

The full details of the U.S. offer to Poland have not been made public but Polish Prime Minister Donald Tusk said on Friday it included putting Patriot batteries on Polish soil for one year, a proposal he said did not go far enough.

Russia has condemned the U.S. missile defence plan as a threat to its own security and has threatened to target missiles at Poland and the Czech Republic -- its communist-era satellite states -- if the deployment goes ahead. (Reporting by Gareth Jones)

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