A top secret nuclear review is underway
The US has had a moratorium on underground tests since 1992 and any resumption would be strongly criticised by allies who favour a worldwide testing ban.
But the Washington Post reported on Tuesday that the highly classified Nuclear Posture Review may raise the possibility of a resumption, said to be necessary to keep ageing weapons safe.
Mr Rumsfeld said the review "certainly doesn't recommend resuming testing".
But, speaking before the Bush administration was due to lay out its nuclear thinking to Congress, he was less definite about how long the moratorium would last.
"Any country that has nuclear weapons has to be respectful of the enormous lethality and power of those weapons, and has a responsibility to see that they are safe and reliable.
"To the extent that can be done without testing, clearly that is the preference. And that is why the president has concluded that, thus far, that is the case," Mr Rumsfeld said.
Two-year timetable
The Washington Post report said the administration wanted to have testing re-allowed without having to announce an end to the moratorium.
Administration officials were reported to want to be able to resume testing quicker than the present two-year timetable allows.
The administration was due to lay out to Congress on Tuesday its thinking behind President George W Bush's announcement last November that the US aimed to cut its nuclear warheads from about 6,000 to between 1,700 and 2,100.
Since taking office Mr Bush has said he favours continuing the moratorium.
However, when he was running as a candidate for president, Mr Bush said he supported the Senate's 1999 decision not to ratify the Comprehensive Test Ban Treaty, designed to put in place a worldwide ban on testing.