WASHINGTON, July 21 (Reuters) - A Republican senator unhappy with U.S. policy on Honduras delayed on Tuesday a committee vote to confirm the nominee to head the State Department's bureau of western hemisphere affairs.

Conservative Senator Jim DeMint, who has expressed concern over Washington's call for ousted Honduran President Manuel Zelaya to be reinstated, invoked his right to ask the Senate Foreign Relations Committee to postpone voting to confirm Arturo Valenzuela, currently a professor at Georgetown University, to be assistant secretary of state.

DeMint also asked for a delay in confirming Thomas Shannon as U.S. ambassador to Brazil. Shannon currently holds the assistant secretary's post.

Both votes had been set for Tuesday afternoon but are now likely to be held next week.

DeMint is one of 17 Republican senators who wrote to Secretary of State Hillary Clinton this month asking the administration to reassess its stance on Honduras.

The group said it worried that Washington's pro-Zelaya stance would legitimize "abuses of power" and "violations of the Honduran constitution" by Zelaya before he was ousted by the army on June 28.

Efforts to broker an end to the Honduran power struggle collapsed on Sunday, after interim leader Roberto Micheletti rejected a proposal to reinstate the overthrown president.

Clinton spoke to Micheletti by phone after the talks fell apart and warned him he could face cuts in economic aid unless he strikes a deal with his rival.

DeMint and other Republicans have said they believe Hondurans were acting lawfully when they ousted Zelaya after he had sought to hold a referendum on overhauling the constitution to allow his re-election.

A spokesman for DeMint said on Tuesday the senator was also displeased at Valenzuela's refusal to discuss Honduras at length during his nomination hearing.

At the hearing, DeMint asked why Washington would want to be on the same side as Venezuela's Hugo Chavez and Cuba's Fidel Castro, in the Honduran crisis.