A battalion of Marines trained for counterterrorism and other complex missions probably will be sent to Afghanistan soon, perhaps this week, a senior U.S. official says. 

As many as 1,500 of the Marines would join Army and Air Force special operations troops already in Afghanistan, the official said Monday. The Marines could provide security for other U.S. forces or expand the search for Usama bin Laden and members of his Al Qaeda terrorist network.

Pentagon officials have not made a final decision on sending in the Marines, the official said, nor have they determined how many troops would be sent and for what tasks. A small advance team might slip into Afghanistan first to arrange for the others' arrival, said the official, who spoke on condition of anonymity.

Two Marine units are waiting aboard ships in the nearby Arabian Sea.

Sending in the Marines would substantially increase the number of U.S. troops on the ground inside Afghanistan. Several hundred U.S. special forces are there now, Defense Secretary Donald H. Rumsfeld has said. The forces, including Army Green Beret and Delta Force units, are in Afghanistan helping anti-Taliban groups and searching for Al Qaeda leaders.

That hunt already has had some success. A Nov. 14 airstrike on a building outside the capital of Kabul killed Al Qaeda's military chief, Mohammed Atef. The strike also killed another 50 Al Qaeda members, several senior Taliban officials and an undisclosed number of Taliban fighters, said another U.S. official, also speaking on the condition of anonymity.

The Pentagon also plans to send additional troops into northern Afghanistan soon to work with other nations' forces in protecting a land route for humanitarian relief, other officials said Tuesday.

The U.S. Central Command is still working out details, including how many U.S. troops may be needed to repair and secure roads, even as it steps up the search for bin Laden and other senior Al Qaeda members.

Victoria Clarke, Rumsfeld's spokeswoman, said the extra U.S. troops may include engineers for road repairs and explosives experts to clear mines and booby traps in the vicinity of Mazar-e-Sharif.

Rear Adm. John Stufflebeem, deputy director of operations for the Joint Chiefs of Staff, said U.S. officials don't know whether bin Laden is still in Afghanistan. Stufflebeem said U.S. bombing continues to target caves and tunnels thought to be used by Al Qaeda leaders.

The Pentagon is considering sending Marines who are part of Marine Expeditionary Units, groups of about 2,200 fighters, pilots and support staff trained to be the first large units to respond to a military crisis. Each unit is anchored by a battalion of about 1,500 Marine infantry troops, who are supported by groups of attack and transport helicopters, fighter jets and armored vehicles.

Both units have special training for missions such as urban combat, counterterrorism and quick-strike ground assaults.

One is the 15th Marine Expeditionary Unit from Camp Pendleton, Calif., which is based on the USS Peleliu and its support ships. Helicopters from that unit retrieved an Army Black Hawk helicopter that crashed in Pakistan last month, then briefly had to abandon it at a Pakistani airfield when unidentified assailants opened fire on the Marines.

The other unit in the Arabian Sea is the 26th Marine Expeditionary Unit from Camp Lejune, N.C., based on the USS Bataan. The unit participated in the Operation Bright Star training exercise in Egypt last month that brought together soldiers from several nations in the region.

The United States is not participating in negotiations between anti-Taliban forces and the Taliban and Al Qaeda troops under siege in the northern city of Kunduz, Stufflebeem said.

Negotiations with the Taliban commander of Kunduz aim to secure the surrender of the city of 100,000 and stave off what threatens to be the bloodiest battle yet of the Taliban's collapse.

Rumsfeld has said he is against any deal that would allow Taliban or terrorist forces to escape to do harm in another country another day. But Stufflebeem said Tuesday that bombing could be halted if opposition forces asked.

The Pentagon released transcripts of two radio broadcasts touting $25 million in reward money for information leading to the location or capture of bin Laden or Ayman al-Zawahiri, a top bin Laden lieutenant. The broadcasts are being made from transmitters aboard EC-130 Commando Solo airplanes.

The U.S. military also is distributing leaflets touting the reward.