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WASHINGTON, April 22 (Reuters) - The Bush administration plans to brief U.S. lawmakers behind closed doors this week about North Korea's suspected nuclear cooperation with Syria, congressional sources said on Tuesday.

It was not immediately clear why the administration wanted to give the briefings -- which are expected on Thursday -- about a topic the White House has kept under wraps since Israel conducted a mysterious Sept. 6 air strike in Syria.

The New York Times reported last year that the strike was aimed at a site intelligence analysts judged was a partly built nuclear reactor, apparently modeled on one North Korea has used to create its stockpile of nuclear weapons fuel.

Lawmakers, including two members of U.S. President George W. Bush's Republican party, have argued that the allegations North Korea may have assisted Syria in an effort to develop nuclear expertise deserved a wider airing in Congress.

The issue is particularly of concern as the United States seeks to persuade North Korea to make an overdue declaration of its nuclear programs as part of a multilateral deal under which Pyongyang agreed to abandon all nuclear weapons and programs. (Writing by Arshad Mohammed, editing by Jackie Frank)

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