Even as the US Senate approved a new nuclear disarmament treaty with Russia, the Pentagon was asking Congress for authority to develop a new generation of tactical nuclear weapons.
Strategic arsenals are to be reduced
The US military believes that the new tactical nuclear weapons are essential to meet to threat of terrorism and weapons of mass destruction, and says they could be used against chemical or biological weapons facilities and nuclear bunkers buried deep underground.
But arms controls advocates say that the plans could undermine US efforts to limit nuclear proliferation at a time when North Korea, among others, seems intent on developing nuclear weapons.
"I don't see how we can look all the nuclear wannabes in the face... when we are going to now launch ourselves into a whole series of new weapons," said Congresswoman Ellen Tauscher, a member of the House of Representatives Armed Services Committee.
The new weapons under consideration include low-yield tactical nuclear weapons, which were banned by Congress in 1993, and a "robust nuclear earth penetrator", designed to bury deep into the ground before exploding.
Senate treaty approved
In a separate action, the US Senate approved, by a vote of 95-0, the strategic arms reduction treaty between the United States and Russia, which was negotiated between President Bush and President Putin at their Moscow summit in June 2002.
Arsenals and Treaties
1972: US and USSR sign first arms pact, but weapons arsenals keep growing
1986: Soviet stockpile reaches its height
1987: Deal agreed to eliminate short and medium-range weapons
1987-1993: USSR slashes short and medium-range weapons by half, the US reduces its arsenal by 72%
1993: US signs a treaty to cut strategic long-range warheads with the nuclear states of the former Soviet Union
Click here for details of nuclear arsenals and treaties
The treaty aims to reduce the strategic nuclear arsenals of Russia and the US from current levels of between 6,000 and 7,000 to between 1,700 and 2,200 over the next 10 years.
But unlike previous arms control treaties, it does not require the actual destruction of the weapons, leading to fears that they could be retargeted or might fall into the hands of terrorists.
The treaty still has to be approved by the Russian Duma.
It followed the US decision to deploy anti-ballistic missiles, forcing the abandonment and renegotiation of a series of arms control deals originally signed with the former Soviet Union.
The Bush administration has told Congress that it wants to spend $21m to develop the nuclear earth penetrator, which could be used against potential enemies who bury their war-making facilities underground.
These could include North Korea, which is suspected of hiding its nuclear production sites in areas carved out of mountains.
The US used nuclear weapons against Japan to end World War II
Everet Beckner, deputy head of the National Nuclear Security, said that the research "might culminate in an integral flight or laboratory test".
The new bomb would be based on the one remaining US tactical nuclear weapon, the B61, with a strengthened nose cone to allow it to penetrate frozen soil or rocks.
Additionally, the Bush administration plans to ask Congress to lift the ban on the development of even smaller nuclear weapons, with yields of under five kilotons, which could be used against above-ground weapons production facilities.
This new generation of nuclear weapons would take longer to develop, and might require underground testing.
Stephen Schwartz, publisher of the Bulletin of the Atomic Scientists, a magazine that tracks nuclear proliferation issues, said that he "could not imagine anything more counter-productive" if the government was interested in preventing the spread of nuclear weapons.
He said that reversing the long-standing ban on the development of tactical nuclear weapons was "stupid, dangerous and irrational", and that even the military itself did not want battlefield nuclear weapons.