Defense Secretary Robert Gates is weighing a possible temporary expansion of the US army to ease the strain from wars in Afghanistan and Iraq, his press secretary said on Wednesday.

Gates was discussing the idea, backed by Senator Joseph Lieberman, with senior officers to add 30,000 troops to the active-duty army, press secretary Geoff Morrell told reporters.

The possible expansion from the current strength of 547,400 would be designed "to get them through what is still a stressful period as we draw down in Iraq and continue to plus-up in Afghanistan," Morrell said.

"So he is engaged in discussions with a number of people about that possibility," he added.

Any expansion would be temporary but would carry a significant price tag, possibly more than a billion dollars, army officials said.

General Peter Chiarelli, the army's vice chief of staff, has told lawmakers that at any given time about 30,000 Army troops in the current force are not available to deploy to combat missions.

About 10,000 army personnel are wounded and receiving medical care, another 10,000 are in training programs and the remainder have been ordered to serve the Defense Department or other agencies and cannot be pulled from their duties.