The Pentagon is preparing to send at least 3,000 marines to Afghanistan in April to bolster efforts to hold off another expected Taliban offensive in the spring, military officials said Wednesday.

The move represents a shift in Pentagon thinking that has been slowly developing after months of indicating that the United States was not inclined to fill the need for as many as 7,500 more troops that commanders in Afghanistan have requested.

U.S. Defence Secretary Robert Gates pressed NATO allies to contribute the extra forces instead.

Canada already has about 2,500 troops in Afghanistan, most in the southern province of Kandahar, and has pushed for more U.S. troops for months.

Pentagon Press Secretary Geoff Morrell said Wednesday that a proposal will go before Gates on Friday that would send a ground and air marine contingent as well as a marine battalion — together totalling more than 3,000 forces members — to southern Afghanistan for a "one-time, seven-month deployment."

Gates will want to review the request, Morrell said, and is not likely to make a final decision on Friday.

"He will take it and consider it thoroughly before approving it," said Morrell. "I just want to get people away from the idea that this is going to be imminently approved by the secretary."

Gates "has some more thinking to do on this matter because it's a serious allocation of forces," he said.

Morrell added that Gates's thinking on the issue has "progressed a bit" over time as it became clear that it was politically untenable for many of the NATO countries to contribute more combat troops to the fight.

"The commanders need more forces there. Our allies are not in the position to provide them. So we are now looking at perhaps carrying a bit of that additional load," the spokesman said.

Morrell said the move was aimed at beating back "another Taliban offensive" that is expected this spring, as has occurred in previous years.

Canada asks for more equipment

When Gates was in Afghanistan last month, commanders made it clear they needed the additional forces.

Canada also has made a point of asking the United States to consider sending more troops to Afghanistan.

Foreign Affairs Minister Maxime Bernier raised the issue in December when he met with Secretary of State Condoleezza Rice and other U.S. officials.

Canada is also requesting more American equipment, such as helicopters and unmanned aerial vehicles.

Currently there are about 27,000 U.S. troops in Afghanistan, including 14,000 with the NATO-led coalition. The other 13,000 U.S. troops are training the Afghan forces and hunting al-Qaeda terrorists. The U.S. led the 2001 invasion of the country.

Morrell said that while the marine ground and air contingent would be put in place to prevent a spring Taliban offensive, the marine battalion likely would be used to train Afghan forces.