Defense Secretary Robert Gates on Tuesday authorized the deployment of about 3,200 U.S. Marines in April to meet an expected surge in Taliban violence, raising the number of American personnel there to around 30,000. U.S. officials say they had to act because European allies weren't filling the shortfall in combat units.

Several European governments have voters who harbor misgivings about President Bush's war on terrorist groups and don't want their troops on the front lines. Some also have troop commitments in Africa, the Balkans and the Middle East and are under pressure to do more for peacekeeping in Darfur.

The refusal to deploy to Afghanistan's dangerous south and east has opened a rift with Britain, Canada, the Netherlands and others which, along with the United States, have borne the brunt of Taliban violence.

The United States contributes one-third of the 42,000-strong NATO mission, making it the largest participant, on top of the 16,000 U.S. troops operating independently. Of the new troops, 2,200 will join the NATO force. The other 1,000 are instructors who will be in a separate U.S. force that trains Afghan forces and searches for al Qaeda fighters.

Washington is adamant that sending the Marines won't let the allies off the hook. It stresses the new Marine deployment will be for only seven months to reinforce NATO's International Security Assistance Force over the spring and summer "fighting season."

Turkey has NATO's second-largest military but keeps just 1,200 soldiers in Afghanistan, based around Kabul. The Turks argue they are under no obligation to do more, since they get no international support for their war against Kurdish insurgents.

Some allies actually make a bigger proportional contribution than the United States. The United States has 1.1 percent of its troops serving with NATO in Afghanistan, while Britain has 4 percent, Denmark 3.5 percent, the Netherlands 2.9 percent and Canada 2.6 percent.

France, traditionally wary of NATO, is taking a changing stance under President Nicholas Sarkozy, who hinted last month that France's contingent of 1,300 could be strengthened.

Sarkozy has agreed to deploy Mirage warplanes from Tajikistan to a NATO base in southern Afghanistan and to send 150 military experts into the south for the first time to train Afghan army units.

NATO diplomats hope Britain will increase its contribution in Afghanistan as it scales down operations in Iraq.

Poland recently announced it would add 400 soldiers and eight much-needed helicopters to its contingent of 1,140, despite an opinion poll in December that said just over 80 percent of Poles opposed participation.

Germany's more than 3,000 soldiers and Italy's 2,550 put them among the biggest contributors to the NATO force, but they bar their troops from fighting in the front-line provinces.