WASHINGTON, March 24 (Reuters) - U.S. Deputy Secretary of State John Negroponte will visit Pakistan this week and hopes to meet newly elected Prime Minister Yousaf Raza Gilani and other officials, a U.S. official said on Monday.

The official, who spoke on condition he not be named, said Negroponte is likely to see President Pervez Musharraf, whose popularity has eroded over the last year and whose political allies were soundly beaten in Feb. 18 parliamentary elections.

Negroponte, a former U.S. director of national intelligence and U.S. ambassador to Iraq, has become one of the key U.S. officials managing Washington's relationship with Islamabad.

He is expected to arrive in Pakistan on Tuesday, one day after Gilani, a loyalist of assassinated opposition leader Benazir Bhutto, was elected by the national assembly and ordered the release of judges Musharraf detained in November.

In a challenge to the increasingly isolated Musharraf, Gilani ordered the immediate release of judges detained after the president declared emergency rule and also called for a U.N. investigation into Bhutto's assassination on Dec. 27.

The incoming coalition partners have pledged to pass a resolution to reinstate the judges Musharraf dismissed out of fear they would rule unconstitutional his own re-election in October by the previous assembly.

If reinstated, the judges are expected to take up legal challenges to the president.

The United States and other Western allies fear more instability in their nuclear-armed ally, facing a campaign of attacks by al Qaeda-inspired militants, if there is confrontation between Musharraf and the new government. (Reporting by Arshad Mohammed, editing by Todd Eastham)

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