WASHINGTON - US DEFENCE Secretary Robert Gates describes his job sending young soldiers off to war as a 'painful thing' in a television interview to be broadcast on Sunday.

'The truth of the matter is, being secretary of war in a time of war is a very painful thing,' Mr Gates told the CBS network's '60 Minutes' program, which released excerpts of the interview.

Mr Gates, appointed by former president George W Bush in 2006 and reappointed by President Barack Obama in 2009, is presiding over a major troop buildup in Afghanistan with the US force due to reach up to 68,000 by the fall, up from about 31,000 in December.

Explaining why he agreed to stay in the post through two successive administrations, Gates said he felt a sense of obligation to the troops.

Mr Gates, a former CIA director, has at times scolded the Pentagon bureaucracy and lawmakers in Congress for focusing on major weapons systems from the Cold War-era instead of the immediate needs of soldiers fighting wars in Iraq and Afghanistan.

Comparing the two presidents he has served as head of the Pentagon, Mr Gates told CBS that Mr Bush was 'committed, questioning and eager to make a decision and move on.' As for President Obama, Mr Gates said the new president was 'deliberative, decisive and calm'.

The program was filmed mostly during Mr Gates's visit to Afghanistan this month. After his return, Mr Gates made the surprise announcement that he had sacked the commander of US and NATO forces there, saying it was time for 'new thinking' in the fight against a growing insurgency.

Mr Gates said it was too soon to say when US troops might be able to withdraw, but he said it would hinge in part on progress in expanding and training Afghan security forces. -- AFP