Washington ? President Bush nominated State Department official John R. Bolton to be U.S. ambassador to the United Nations Monday, selecting an administration loyalist who has disparaged the world body and clashed with allies over Iran and North Korea policy.

Bolton’s approval seemed assured by the Republican majority in the Senate. But with congressional Democrats expressing dismay over his selection, the confirmation hearing may be rancorous.

In announcing Bolton’s nomination, Secretary of State Condoleezza Rice called Bolton a “tough-minded diplomat” who had developed a “proven track record for effective multilateralism” as undersecretary of state for international arms control and nonproliferation, a post he has held since 2001.

“He knows how to get things done,” she said.

Bolton acknowledged Monday that his previous criticism of the United Nations was likely to raise concerns in some quarters. Among his controversial comments was a 1994 remark referring to U.N. headquarters.

“The Secretariat building in New York has 38 stories. If it lost 10 stories, it wouldn’t make a bit of difference,” he said. And in 2000, Bolton told National Public Radio that the U.N. Security Council needed only one permanent member, the United States, “because that’s the real reflection of the distribution of power in the world.”

But Bolton pledged to work cooperatively with Congress and other nations. “Working closely with others is essential to ensuring a safer world,” he said Monday.

Bolton’s nomination took many on Capitol Hill by surprise. Senate Foreign Relations Committee Chairman Richard Lugar, R-Ind., who must preside over the confirmation hearing, declined to voice support for Bush’s choice. Lugar wants to meet with Bolton “before discussing his support,” Lugar spokesman Andy Fisher said.

Democrats criticized the choice. “This is just about the most inexplicable appointment the president could make,” said Sen. John F. Kerry, D-Mass. “If the president is serious about reaching out to the world, why would he choose someone who has expressed such disdain for working with our allies?”