OVER THE NORTH SEA, Oct 25 (Reuters) - The United States has gone as far as it can to win Russia's cooperation on a missile shield in Europe, U.S. Defense Secretary Robert Gates said on Thursday after offering to put the system in a stand-by mode.

"I think we've leaned about as far forward as we can," Gates told reporters on a U.S. military aircraft en route to Washington. "We've offered a lot and my view is now I want to see some movement on their part."

Washington wants to place missile defence assets in the Czech Republic and Poland as part of shield to defend against missiles from "rogue states" such as Iran and North Korea. But Moscow says the system threatens Russian security.

Gates on Tuesday said the United States had proposed to build the sites but place them in a stand-by mode pending proof of a missile threat. He said that was offered to the Russians in a bid to ease Moscow's opposition and encourage its cooperation.

He also said Washington offered to give Russia some presence at the sites, to promote transparency.

"I think the question is whether the Russians are serious about partnering with us, or whether this is merely a pose to try and stop us from going forward with the Czech Republic and Poland," Gates said.

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