US Defense Secretary Robert Gates told US troops in Iraq Thursday their wages could be delayed due to a budget deadlock in Washington, joking that "guys with guns" get paid first.

"First of all, let me say you will be paid. It's occurred to me all smart governments always pay the guys with guns first," he joked during an inspection of some of the nearly 50,000 US troops remaining in Iraq.

A deadlock between Republicans and Democrats in Washington threatens to shut down vast parts of the US government, forcing combat troops and others to go without pay if no breakthrough is found by Friday evening.

"If the government shutdown starts on the 8th and goes for a week, you'd get half a cheque. If it goes from the 15th to the 30th, you wouldn't get a cheque on the 30th but you would be backpaid for all of it," Gates told troops at the Camp Liberty US military base west of Baghdad.

US military personnel are paid on the 15th and 30th of each month.

"Frankly, I remember when I was your age I did a lot of living from paycheque to paycheque, so I hope this thing does not happen, because I know it would be an inconvenience for a lot of troops," Gates said.