WASHINGTON - Faced with a budget cut of nearly $500 billion over 10 years, the United States has decided to trim its ground troops but will create a "cutting-edge force" for tactical operations to protect American interests.

As per the new announcement by US Defence Secretary Leon Panetta, 100.000 troops will have to go, mostly from the army.

He said the size of the active-duty army will fall to 490,000 over five years, down 80,000 from its wartime peak of 570,000 in 2010.

The marines will lose some 20,000 personnel, he noted at a Pentagon news conference announcing the defence budget.

The downsizing of US military comes as Pentagon is facing cuts of $487bn (310bn) over the next 10 years.

"We plan to gradually resize the active army," said Panetta.

"The active Marine Corps will go to 182,000. That's down from 202,000. That transition will take place over the five years. We won't reach those numbers until 2017."

The defence secretary said the US would boost special forces and retain the ability to defeat "any enemy on land."

"The military will be smaller and leaner, but it will be agile, flexible, rapidly deployable and technologically advanced. It will be a cutting-edge force."

He said the focus would shift from large-scale conflicts in Iraq and Afghanistan to areas of key national interest, including a strengthened commitment in Asia.

Some members of Congress did not agree that such a budget would maintain a strong US military.

"Taking us back to a pre-9/11 military force structure places our country in grave danger," said Texas Senator John Cornyn, a member of a committee that will hold hearings on the budget plan.