President George W Bush will tonight seek to reassure an anxious world that he is keen, if at all possible, to pursue diplomacy to resolve the crises over the nuclear programmes of Iran and North Korea.

In his annual State of the Union address, Mr Bush will make clear that "diplomacy is very much at the forefront" in dealing with the countries, a senior administration official said last night.

"I´ve noticed many people don´t pay attention to the words the president has used," the official said. "He has demonstrated time and time and time again ... that diplomacy is the most effective way to convince Iran that the path they are taking is not the best way to join the community of nations."

Mr Bush said last month that America´s mission was to spread freedom "to the darkest corners of the world". That address was widely interpreted abroad as laying out an explicitly interventionist agenda, sparking speculation that the administration was considering taking military action against Iran.

But ever since then the administration has been qualifying Mr Bush´s words, a process that will be completed tonight in his address to a joint session of Congress.

"The work of ending tyranny doesn´t happen overnight," the official said, adding that the phrase "outposts of tyranny" used by the new secretary of state, Condoleezza Rice, of six rogue nations, including Iran and North Korea, will not be repeated tonight.

Mr Bush will make much of Sunday´s elections in Iraq, hailing them as proof of the success of his mission to spread freedom in the Middle East. But he will not answer Democratic calls for an explicit exit strategy for United States troops in Iraq.

While emphasising diplomacy, his 40-minute speech will be far from apologetic on his muscular foreign policy.

The address comes after reports that the Pentagon is proposing to revive a controversial programme to build nuclear warheads capable of penetrating hardened underground targets such as Iran´s covert nuclear facilities.

A leaked memo from Donald Rumsfeld, the United States defence secretary, to the energy department proposed funding for the scheme to begin next year. "You can count on my support for your efforts to revitalise the nuclear weapons infrastructure and to complete the RNEP (robust nuclear earth penetrator) study," Mr Rumsfeld wrote in a memo seen by the Washington Post.

The leak seems certain to trigger a major row with Congress, which eliminated the scheme from the budget last year, angered by estimates suggesting the programme would cost more than $500 million (£265 million).

The administration has long emphasised that the scheme is merely a question of research and that Congress would have to approve the production of such weapons.

In his address tonight, Mr Bush will also call for a near-freeze in the overall growth of government spending not connected with defence to try to rein in record deficits. (© Copyright of Telegraph Group Limited 2004. 02/02/05)