WASHINGTON – As Iran moves closer to obtaining a nuclear weapon, the Pentagon has started eyeing construction of a new military base near the Iran border in western Afghanistan.

American officials confirmed yesterday to The New York Sun that the military has begun scouting out an area in the Holang desert area of the Herat province within 20 miles of the Iran border. Two administration sources familiar with the plan said the base would be largely for the Afghan army but that American aircraft would probably be deployed there as well.

The development could give America and its allies more military options should the president decide to use force to delay or still the Persian nuclear program. In many ways, American forces have effectively encircled Iran, projecting power not only from a coalition base in Kirkuk, northern Iraq, but also from military facilities in Uzbekistan. Those facilities were initially leased for Operation Enduring Freedom shortly after the September 11, 2001, attacks on New York City and the Washington area. In addition, the American Navy still patrols the Persian Gulf sealanes, making it possible to bring an aircraft carrier into those shallow waters off the coast of the Islamic republic.

The story of the new base in Afghanistan was first reported November 27 by the Pakistan Daily Times, which quoted local residents as saying they had seen American military personnel surveying the area for an airbase of about 300 hectares – the equivalent of about 750 acres – in the Holang desert. The story quoted Afghan officials as saying the base was for training the new national army, as America and many European countries have pledged to do. The dispatch quoted a spokesman for President Karzai, Javid Ludin, as saying, “The coalition forces have the permission to act against terrorism and for the peace and stability of Afghanistan, and to build a base for that purpose.”

The primary terrorism problem in Afghanistan is associated with the remnants of the Taliban and al Qaeda, who are said to be concentrated largely at the Afghan border with Pakistan. After the war, coalition forces ceded control of the Herat province, location of the proposed airbase, to Ismail Khan, who was friendly to Iran and allowed the Iranians to place religious police in the city shortly after the fall of Kabul. Mr. Khan, who still commands a largely Tajik militia, was sacked in September by Mr. Karzai in an effort by the president to rein in the regional warlords empowered after the coalition victory in 2002.

Iran was initially brought into reconstructing Afghanistan after the collapse of the Taliban government. At a conference in Bonn in 2002, the Iranians promised to deliver the cloth for the new Afghan army’s uniforms, and for a while Iran had built more roads in Afghanistan than America and the United Nations.

But the American policy of reaching out to Iran has changed in recent months, as Washington has concluded that Iran is much closer to building a nuclear bomb than it originally believed, leading some senior officials to predict it is less than two years away. President Bush’s choice to succeed Colin Powell as secretary of state, Condoleezza Rice, told Jewish leaders at the White House last Monday that the president would not tolerate the Islamic republic’s obtaining an atomic weapon, according to two people who attended the meeting.

On December 3, the outgoing deputy secretary of state, Richard Armitage, said, however, that the best recourse for Iran was to approach the nuclear aspirations of the ruling mullahs through diplomacy. In an interview broadcast on the Australian Broadcasting Corporation, Mr. Armitage said he did not believe the current Iranian program could be deterred through a unilateral military strike, similar to Israel’s strike on Osirak, Iraq, in 1981.

“The Iranian situation doesn’t lend itself to an Osirak solution as we saw in 1981,” he said. “Many of the facilities are underground or disguised, and you could never be sure that if you took such a chance that you would get any, much less most, of the Iranian nuclear program. The best way to resolve this is through diplomacy.”

Late last month, the International Atomic Energy Agency announced that it had struck a deal with the Iranians to end enrichment of uranium in exchange for increased European cooperation with a program the Islamic Republic has insisted is intended only for the production of atomic energy.

Emboldened by the deal, Iran has be gun diplomatic posturing on the issue. Last week, the director general of the U.N. watchdog agency, Mohammed El-Baradei, said he had become aware of two more sites that could potentially be used for enrichment activities but were not covered in the new agreement. Over the weekend, the powerful former president, Akbar Hashemi Rafsanjani, told the state-run television that he did not expect the government to keep the enrichment deal more than six months. The spokesman for the foreign ministry, Hamid Reza Asefi, said he expected the suspension of enrichment would last only a “short while,” according to wire services.

Mr. Asefi called on the European Union yesterday to crack down on anti-Muslim bigotry, in response to recent outrage in the Netherlands over the murder of Theo van Gogh, the Dutch auteur, who was murdered November 2. Van Gogh’s film, “Submission,” told the story of a Muslim woman forced into a marriage and raped by her uncle. The movie provoked a Moroccan fundamentalist to stab and shoot van Gogh. “In the Netherlands,” the Iranian said, “we see somebody’s appalling act has provoked Muslims, and this has been followed by harsh measures being taken by anti-Islamic circles.”