THE US government is planning to undertake the most costliest modernization ever of its nuclear arsenal, even though the military as a whole is facing stiff spending cuts.

There was no official price estimate for the effort to upgrade and maintain the 5113 warheads in the inventory, replace old delivery systems and renovate the ageing nuclear facilities, the Washington Post reported.

But a study during the northern summer by the Stimson Centre, a Washington think tank, estimated that costs would be at least $US352 billion over the coming decade, the report said.

Others said the figure could be far higher, particularly if the work was delayed even longer, the paper said.

Upgrading just one of the seven types of weapons in the stockpile, the B61 bomb, was likely to cost $US10 billion over five years, the Post reported.

It would cost up to $US110 billion to build 12 replacements for the ageing Ohio-class submarines, the paper said, citing estimates by the US Congressional Budget Office.

According to the report, the Minuteman III ballistic missiles are undergoing a $US7 billion upgrade.

At the same time, a nuclear-capable fleet of F-35 strike aircraft is being built to replace existing aircraft at a cost of $US162 million per plane, the paper said.

Modernising the buildings and laboratories where the refurbishments would take place was expected to cost at least $US88 billion over 10 years, it said.