WASHINGTON, Sept 9 (AFP) Key lawmakers in the US Senate on Tuesday supported a Pentagon decision to extend the tours of duty for thousands of National Guard and Army Reserve troops in Iraq, while critics condemned the move as the latest proof of shoddy US military planning.

The US Army announced Tuesday it would extend the current 12-mon th mobilization of Army Reserve by between three to six months.

"It means our Reserve forces will be mobilized longer than initially planned, but we believe this is a measured and responsible decision by the army and a decision that will contribute directly to improving stability in Iraq," said US senators Zell Miller and Saxby Chambliss, co-chairs of the Senate's Reserve Caucus.

Reserve and National Guard troops, who train one weekend a month and two weeks a year, were once mainly used to provide help in their home states after local emergencies like riots or floods.

But with active-duty forces stretched thin by the war on terror and the occupation of Iraq, Guard and Reserve units now face a good chance of lengthy tours of duty overseas.

"We encourage the army and the Department of Defense to continue utilizing the Reserve components wisely," Miller and Chambliss said in a statement.

Army officials have defended the new policy, saying that the scarcity of active-duty forces and security concerns make it necessary to keep a large number of Guard and Reserve troops in Iraq for as long as possible.

Critics, however, said the extended deployments are likely to have a negative impact on morale, retention and recruiting.

"It is outrageous that our heroic 'citizen soldiers' are going to have to pay the price of the administration's poor military planning and failed diplomatic efforts -- both of which have caused our current troop shortage," said Senator Frank Lautenberg, a Democrat from New Jersey.

"This will make it even more difficult for reservists, their families and the small businesses where they work to endure the hardships associated with serving our nation," said Senator John Kerry of Massachusetts, who is also running for the White House.

Kerry introduced legislation Tuesday to provide a tax credit to small business owners who employ a reservist called up for active duty. He said the policy change added to an already disproportionate burden borne by individual families and small businesses.

"The president's inability to work with the international community and win the peace has put an additional strain on our reservists," the Massachusetts Democrat said.

The policy change coincides with a drive by the US government to recruit more international troops for deployment in Iraq, amid fears that US forces are stretched to breaking point with deployments in Iraq, Afghanistan and elsewhere around the globe.

Of 122,000 US troops currently deployed in Iraq, according to media reports, 3,000 belong to the National Guard and 5,000 are reservists. Another 5,000 guards and 7,000 reservists are serving in Kuwait.