GENEVA (Reuters) - The United States and the European Union Tuesday expressed their frustration that attempts by the U.N. arms control body to halt the production of nuclear bomb-making fissile material had again foundered.

``Yet another year has passed without any material progress to show to the international community,'' U.S. disarmament ambassador Robert Grey lamented in a speech to the U.N. Conference on Disarmament.

He called on all states to show flexibility in 2000 to allow work to begin on the fissile material ``cut-off'' treaty, which Washington sees as the next step in nuclear disarmament.

``It's the only hope we have of avoiding yet another sterile year on the multilateral arms control front and for beginning the new millennium with a solid and full-scale arms control program of work,'' Grey said.

Washington and the EU urged the Conference to launch negotiations to halt production of fissile material (plutonium and highly-enriched uranium) as soon as the talks resume in Geneva in January.

Despite growing fears of a nuclear arms race between arch-foes India and Pakistan, envoys and U.N. sources saw little prospect of the 66-member body breaking the stalemate quickly.

Finland's Ambassador Markku Reimaa, speaking on behalf of the 15-member EU and 10 associated countries of Central and Eastern Europe, said: ``The fissile material cut-off treaty has been the long-standing goal of the international community.

``The European Union is convinced that a fissile material cut-off treaty, by irreversibly limiting the fissile material stockpiles available for use in nuclear weapons and by establishing an effective verification system, will strengthen the international nuclear non-proliferation regime...''

France's disarmament envoy, Hubert de la Fortelle, said: ''The conclusions of this year are disquieting. The tyranny of inertia carried the day over the will to act.

``Prospects for the 2000 session appear very bleak,'' he added. ``The Conference must avoid, at all costs, a fourth year of paralysis which will contribute to discrediting it further.''

British envoy Ian Soutar regretted the ``totally unacceptable impasse.''

``There simply cannot be nuclear disarmament without confidence that no new fissile material is being produced for nuclear weapons or other nuclear explosive devices.

``A fissile material cut-off treaty is not then the last step, but it is the next essential one,'' he said.

The Conference on Disarmament launched fissile negotiations in August 1998, but never began substantive negotiations. This year, it has been unable to renew the negotiating committee's mandate.

The five official nuclear powers -- Britain, China, France, Russia and the United States -- have refused demands by non-aligned powers including India and Pakistan to go further by launching negotiations to eliminate nuclear arms, diplomats say.

The United States, which is studying plans to develop and deploy a missile defense system, is the only member opposed to negotiations on outer space defense systems.

Washington's firm position has also prevented reaching agreement on a compromise negotiating package at the Conference, according to diplomats.

The only tangible progress in 1999 was agreement to admit five new states -- including Ireland which was kept waiting 17 years to join the world's only multilateral disarmament body.