BISHKEK, Kyrgyzstan, July 25 - Defense Secretary Donald H. Rumsfeld arrived in this Central Asian nation today to shore up an unsettled military basing arrangement here that has been critical to operations in Afghanistan. The refueling and cargo mission operated by the American military from Manas Air Base, just outside the Kyrgyz capital, has been essential to ferry aid, troops and equipment to and from Afghanistan. About 1,000 American troops operate from the airfield, the base for a dozen KC-135 refueling jets and C-130 cargo planes.
But this agreement appeared to be cast in jeopardy earlier this month when Kyrgyzstan and three other Central Asian states joined Russia and China in calling for the United States to set a deadline for withdrawing from the base here and another in neighboring Uzbekistan.
Mr. Rumsfeld told reporters traveling with him en route here from Washington that the status of the bases was a matter of negotiations with the host countries, not the regional alliance, which is known as the Shanghai Cooperation Organization and is dominated by Russia and China.
"We have good arrangements in this part of the world with respect to basing and overflight rights," Mr. Rumsfeld said, referring to other regional states, like Tajikistan. "They have been a great help to Afghanistan and a great help to the global war on terror."
Ten days ago, Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, was even blunter in his assessment of the alliance's demand: "It looks to me like two very large countries were trying to bully some smaller countries."
The fate of the Manas base is especially important given the growing tensions between the United States and Uzbekistan since late May, when Uzbek security forces used gunfire to put down an uprising and anti-government demonstration in Andijon. Many Western governments and organizations have urged Uzbekistan to allow a credible international inquiry into the uprising and crackdown, but President Islam A. Karimov has refused.
Speaking at the start of a three-day trip to Central Asia and other countries, Mr. Rumsfeld said the United States and Uzbekistan have had a good basing arrangement and he was not using the visit to shop around for alternatives. "We're not at that point," he said.
But a senior Air Force officer familiar with operations in the region said the military's Central Command was already examining "work-arounds," military parlance for alternatives, in the event the Pentagon is forced to leave the Uzbek base.
On Tuesday, Mr. Rumsfeld will meet here with President-elect Kurmanbek S. Bakiyev, a former opposition leader who won a landslide victory in the July 10 elections that international observers generally praised for their openness and democratic integrity.
A Defense Department official, speaking on the condition of anonymity to avoid upstaging his boss before the meetings, said Mr. Rumsfeld would brief Mr. Bakiyev and other top Kyrgyz officials on American operations in Afghanistan, the future security outlook there, and what that means for American requirements for access in and out of the region.
During his campaign, Mr. Bakiyev repeated the Shanghai alliance's demand for a deadline to the American presence. But since the election, some of Mr. Bakiyev's aides and other Kyrgyz officials appear to be trying to finesse that position, in what some regional analysts say could be a canny effort to balance the government's foreign policy with Russia, China and the United States. "We have to ensure that our security and economic interests are protected," Kyrgyzstan's Security Council secretary, Miroslav Niyasov, said earlier this month, noting the government's intention to "do its best to avoid spoiling relations with Washington."
The Pentagon is providing about $10 million this year in military aid to Kyrgyzstan, a mountainous, landlocked country of five million people.
Regional security analysts say that Mr. Rumsfeld's visit will be successful if the two countries can come up with a rationale that gives the Kyrgyz public political cover for maintaining operations at the base into the future.
Mr. Rumsfeld visited Kyrgyzstan in April, just weeks after the uprising known as the "Tulip Revolution" forced out the former president, Askar Akayev, who fled the country.