Afghan opposition forces, not U.S. Marines, probably will vanquish the Taliban in their last stronghold of Kandahar, Defense Secretary Donald H. Rumsfeld said.

More than 1,000 Marines have established a base about 70 miles southwest of the southern Afghan city, but Rumsfeld said Tuesday they probably would not be involved in attacking the city.

``We don't have any plans at the present time to be using U.S. forces in that way,'' Rumsfeld said at a Pentagon news briefing.

U.S. warplanes have been bombing Kandahar for weeks to help anti-Taliban attackers. The supreme Taliban leader, Mullah Mohammed Omar, has instructed his followers not to surrender.

``Hiding in the city, the Taliban are in effect using the civilian population of Kandahar as shields,'' Rumsfeld said.

Two main groups of anti-Taliban forces are pressing toward Kandahar as a contingent of about 1,300 Marines operates farther south but within striking distance, Rumsfeld said. Other officials said the Marine contingent may grow to about 1,500 in the days ahead.

``The situation in Kandahar is complicated. It's not easy, but one thing is clear: The Taliban and Al Qaeda will be driven from Kandahar,'' Rumsfeld said. ``The choice really is theirs as to how it happens.''

The Marines' presence, with their vehicle-mounted machine guns, shoulder-fired missiles and attack helicopters, makes it nearly impossible for the Taliban to reinforce or resupply Kandahar, he added.

Air Force Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said at the news conference with Rumsfeld that the Marines have begun blocking or otherwise cutting off roadways leading out of the city. He would not discuss how the Marines are doing this, saying he did not want the Taliban to know.

Another official, speaking on condition of anonymity, said the Marine patrols were aimed not only at stopping the reinforcement of Kandahar but also watching for the attempted escape of Taliban leaders. The official said allied troops, apparently Australian or British, are patrolling with the Marines.

Myers would not say whether the Marines had engaged in combat on these patrols.

The United States is focusing its bombing on Kandahar and the mountainous area near the Khyber Pass south of Jalalabad, where it is believed Usama bin Laden and his top lieutenants are hiding in a complex of caves and tunnels.

U.S. planes also are dropping leaflets in the Jalalabad area of eastern Afghanistan to solicit help in tracking down bin Laden.

Anti-Taliban officials said the United States asked them to repair the runway at the Jalalabad airport so that airplanes could begin landing by Thursday. Pentagon officials said they knew of no plans to use the airport for offensive operations, although a small number of U.S. Special Operations Forces are in that area working with opposition groups in the search for bin Laden.

Rumsfeld said the Bush administration has yet to decide what to do with an American believed to have been fighting alongside the Taliban and who is now receiving medical treatment from U.S. forces in Afghanistan.

The secretary refused to say whether he considers the man, who has identified himself as John Walker, a traitor.

``We found a person who says he's an American with an AK-47 in a prison with a bunch of al-Qaida and Taliban prisoners,'' Rumsfeld said. ``You can be certain he will have all the rights he is due.''

President Bush was asked about Walker when interviewed Tuesday for ABC's 20/20 program.

``We're just trying to learn the facts about this poor fellow,'' he said when asked if Walker was a traitor. ``Surely, he was raised better than to know that a government that suppresses women and women's rights, that doesn't educate young girls, is not the kind of government worth dying for.''

Rumsfeld said he had been told there are two other Taliban fighters in Afghanistan who claim to be Americans. ``People are looking for them,'' he said, adding that he knew nothing else about them.