The Bush administration yesterday dispatched two senior State Department officials for talks with rival factions in Khartoum and southern Sudan to prevent Sudan's fragile peace from unraveling after Vice President John Garang's death in a helicopter crash.

President Bush yesterday hailed Garang as a "visionary leader and peacemaker" who had served as a "beacon of hope" for ethnic and religious groups in Africa's largest country.

In a statement, Bush pledged that the United States remains committed to helping Sudan implement the Comprehensive Peace Agreement signed in January. The pact ended 22 years of warfare between northern Arabs who controlled the central government and a southern faction of Christians and animist Africans led by Garang for two decades.

"Garang's vision of peace must be embraced by all people in Sudan so that they can live in a democratic, peaceful and united country," Bush said. U.S. officials said initial but incomplete information indicates that the crash of the Ugandan presidential helicopter carrying Garang and top aides was due to bad weather rather than foul play.

After increasing involvement in both the peace process and the Darfur crisis, the United States expressed concern yesterday that riots in Khartoum after Garang's death would escalate and renew tensions. Connie Newman, assistant secretary of state for African affairs, and Roger Winter, special U.S. envoy to Sudan, left for the African nation to encourage the parties "to maintain momentum" on efforts toward peace and ending the genocide in Darfur, State Department spokesman Tom Casey announced.

In Khartoum, the U.S. Embassy issued a warning to American citizens to "stay indoors in a safe area," because of disturbances in the capital. Americans considering travel were urged to postpone nonessential visits.

U.S. strategy has rested heavily on Garang. Secretary of State Condoleezza Rice met with him several times, including on her visit to Khartoum and Darfur on July 21. In a statement, she praised his "intellect and energy," and commended Sudan's major parties for recommitting to the peace process in the wake of the leadership crisis.

Over the past five months, Deputy Secretary of State Robert B. Zoellick traveled to Khartoum and Darfur three times to help cement the peace and work on ways to alleviate the separate humanitarian suffering in Darfur, a region where whole villages have been destroyed and thousands displaced.

The State Department said it expects "an orderly and peaceful succession" to the post of first vice president.

But U.S. analysts and international conflict monitoring groups expressed concern about the fallout from Garang's untimely death. The rioting and looting "threaten to further destabilize the situation if not brought under control," the Brussels-based International Crisis Group warned yesterday.

Garang's Sudan People's Liberation Army quickly named deputy Salva Kiir Mayardit as his successor. But experts said Garang had been key to achieving the peace agreement and would not be easily replaced as a leader.

The new crisis in Sudan is "worrisome" because Garang was a "charismatic leader who could bring his ethnic group, the Dinkas, and the whole southern region, with him," said Walter H. Kansteiner III, former assistant secretary of state, now at the Scowcroft Group. "What he did was bold and needed someone who had that ability to pull everyone along with him.

"But the deal is done and everyone has accepted and embraced it. John put them on the right road. He'll always be remembered as the guy who made it happen but there are other people who can implement it," Kansteiner said.

A relative of Sudanese Vice President John Garang grieves as she arrives in New Site village in southern Sudan, where Garang's body had been brought.President Bush called Garang a "visionary leader."