Undersecretary of State Nicholas Burns, a State Department Arabist and a critic of Israel, has emerged as the leading foreign policy official in the Bush administration.

Mr. Burns has by default become the most powerful figure in the State Department and responsible for day-to-day management of U.S. foreign policy. Officials said Mr. Burns was authorized by Secretary of State Condoleezza Rice in late 2005 to become the leading foreign policy administrator amid a sharp decline in support for President Bush.

"Nick Burns has everything Condi doesn't have—a firm sense of purpose, a political fighter and an Arab expert," an official said. "What Burns doesn't share with Condi is the president's agenda."

Officials said Ms. Rice has been preoccupied with recruiting domestic support for the Bush administration. They said she has spent much of her time at the White House advising the president and often serving as a buffer to senior members of the administration.

As a result, Mr. Burns, formally No. 3 in the State Department, has become the de facto director of U.S. foreign policy. Officials said his access to the president has sharply increased over the last four months and Mr. Burns has become a leading adviser to Mr. Bush on Europe and the Middle East.

Mr. Burns was U.S. ambassador to Greece, as well as to NATO in Belgium. He helped end the virtual U.S. boycott of France in 2004. The undersecretary also persuaded the president to adopt the European Union’s policy of dialogue with Iran to end its uranium enrichment program.

"The United States and Europe are natural allies—not identical twins," Mr. Burns told the European Institute last month. "You're more statist—we're more free market. You think of the EU first—we think NATO. We're convinced that the U.S. can win the World Cup—you probably think England or the Czech Republic or Spain will win."

Still, Mr. Burns' agenda is said to sharply differ from that of Mr. Bush's first term. Officials said Mr. Burns has managed to sideline the president's policy to introduce democracy and reform in the Middle East. The undersecretary persuaded Mr. Bush to waive human rights sanctions on a range of Arab and Islamic countries, including Indonesia, Libya, Saudi Arabia and Sudan.

"Condi has very little interest in the Middle East and regards her meetings with some leaders in the area with disdain," an official said. "In contrast, Burns relishes his contacts with Arab leaders."

Mr. Burns has also encouraged Mr. Bush to increase pressure on Israel in an effort to win Arab support for U.S. policy in the Middle East. Officials said the undersecretary has also helped reduce the president's ardor to enact regime change in Iran and Syria.

The ascent of Mr. Burns has come at the expense of the National Security Council, officials said. They said Deputy National Security Advisor Elliot Abrams has lost virtually all of his influence over U.S. policy. Mr. Abrams, who has been linked to the Bush family, has been an ardent supporter of Middle East democracy and Israel. He has urged an aggressive U.S. policy against Iran.

"The major theme that runs through briefings given by Burns is that virtually every conflict in the Middle East is either caused or exacerbated by the Arab-Israeli conflict," the official said. "Not surprisingly, the message to the president is that U.S. support for Israel causes problems for the administration."