ASTANA, Kazakhstan, Dec. 9 — President Nursultan A. Nazarbayev of Kazakhstan urged the United States today to consider the strategic role of Iran as a transport route for the huge crude oil and natural gas deposits under development in the Caspian Sea region of Central Asia.

Since the collapse of the Soviet Union, the United States has maneuvered diplomatically to bolster the independence of the new countries of the Caspian region.

It has been working to secure the region's oil wealth with Western participation and has been promoting new pipeline routes that would skirt Russia and provide an outlet through Turkey, a NATO country, for one of the largest oil reservoirs in Eurasia.

Up to now, American objectives aimed to exclude Iran as a major player in controlling the flow of oil from the region.

Speaking in a news conference with Secretary of State Colin L. Powell, the Kazakh president said his country's oil export potential would quadruple in the next 15 years.

He noted that although American oil companies had advised that the most direct and cost-effective route to send some of that oil to world markets was through Iran, Washington had been unwilling to consider a proposal that would require the lifting of longstanding sanctions against Tehran.

"I say frankly that our investors who work on oil consider that the most beneficial route is through Iran to the Persian Gulf," Mr. Nazarbayev said. "I think that the secretary of state avoided this question on purpose. This is not only my opinion, but in addition American companies think this."

In the course of the antiterror campaign in Afghanistan, in which Iran offered to conduct search-and- rescue missions for any American pilots lost near the Iranian frontier, Secretary Powell has said the United States must seize opportunities for strategic shifts in international affairs. And Iran has been on his mind, he said last month in an interview with The New York Times .

But when Mr. Nazarbayev raised the oil transport issue today, Secretary Powell responded with caution, sticking to the current policy line, first developed by President Clinton: that routes through Russia and Turkey were preferred and sufficient to deal with Caspian Sea oil. Still, he did not rule out the prospect that the Kazakh president had raised.

After breakfast with oil company and other executives at the American Chamber of Commerce here, Secretary Powell said he was "particularly impressed" with "the amount of money they are looking at investing in Kazakhstan."

"They were talking in the range of $200 billion over the next 5 to 10 years," he said, "because they see that kind of potential. To get that kind of potential out, you've got to move it. You've got to move all that fuel or crude and natural gas, and so I heard the president carefully, but I did not have a well-structured answer that I would have contributed at that point or now."

One factor that the United States will have to consider, according to a top adviser to the Kazakh president, is whether Caspian countries will simply turn to Chinese, European or Russian companies more willing to accommodate their objectives.

"We are now rethinking the whole situation in Asia," the adviser said.

The United States lists Iran as a sponsor of terrorism and a nation that is secretly developing nuclear weapons. But the rise of a moderate leader, President Mohammad Khatami, and demonstrations by Iranian youths — some chanting pro-American slogans this fall and advocating democratic reform — have stirred American interest in a new dialogue.

As he flew to Moscow after a two- day visit to Central Asia, Secretary Powell said that setting aside the oil transport question for now, "I am open to explore opportunities."

"We have been in discussions with the Iranians at a variety of levels and in some new ways since Sept. 11," he said, pointing out that James F. Dobbins, the American representative to the new Afghan leadership, had worked with Iranian officials in Bonn during negotiations to form an interim Afghan government.

"And I had a handshake and a brief discussion with the Iranian foreign minister at the United Nations," the secretary added, "so there are a number of things going on."

He said the Bush administration did not have any illusions about the nature of the Islamic republic in Iran, where decision making still is in the hands of hard-line religious leaders, but he added, "We've recognized that the Iranian people are starting to try to find a new way forward, and we're open to exploring opportunities."

Before he left Astana, which replaced Kazakhstan's principal city, Almaty, as the capital in 1997, Secretary Powell announced that Mr. Nazarbayev would visit Washington on Dec. 21 at the invitation of President Bush.

In Moscow, Secretary Powell dined with Foreign Minister Igor S. Ivanov tonight after laying a wreath in Pushkin Square, where a terrorist bomb killed 13 Russians in August last year.

Secretary Powell said he wanted to visit the site to express solidarity with Russia in the fight against terrorism while at the same time urging Moscow to seek a political solution to the long war in Chechnya.

Secretary Powell will meet President Vladimir V. Putin on Monday. The two leaders are expected to make progress on a new strategic arms accord that will reduce each side's nuclear arsenal to about 2,000 warheads from the current level of 6,000.

The secretary indicated that the document would carry forward substantial provisions of the treaties known as Start I and Start II that ensure verification and inspection procedures for the nuclear arsenals.

Secretary Powell said the most contentious issue was an agreement to allow the United States to proceed with robust testing of antimissile systems that would violate the Antiballistic Missile Treaty of 1972.

"They continue to find the ABM treaty at the center of the strategic framework," the secretary said. "We have been unable to persuade them otherwise, and they have been unable to persuade us otherwise."

A State Department official traveling with Secretary Powell insisted that no deadline had been set to resolve the issue, "but increasingly, we are constrained by the treaty" as the Pentagon prepares major missile defense tests in the spring.