U.S. President Barack Obama, left, speaks with his Russian counterpart Dmitry Medvedev on the sidelines of the APEC summit in Singapore in November. The two sides are near a landmark deal to reduce their nuclear arsenals. (Mikhail Klimentyev, Presidential Press Service/Associated Press)

The U.S. and Russia agreed to a historic deal Wednesday to reduce the nuclear arsenals of the former Cold War rivals, the most significant pact in a generation and an important milestone in the decades-long quest to lower the risk of global nuclear war.

U.S. President Barack Obama and Russian President Dmitry Medvedev are to sign the treaty in two weeks in Prague, once final technical details are worked out, officials in Washington and Moscow said.

The landmark treaty would require nations to reduce their number of strategic nuclear warheads to roughly 1,600, well down from the current limits. The New York Times reported Wednesday it would also require both sides to reduce their number of nuclear bombers and sea-launched missiles to 800, down from 1,600 currently.

Obama reportedly wants to bring the total number of allowed warheads down to less than 1,000 each as quickly as possible. Buoyed by the political capital he has accrued by passing his hard-fought health care legislation on Sunday, those farther-reaching agreements are now expected later in his presidency.

Replaces START treaty

The pact would replace the Strategic Arms Reduction Treaty of 1991. START quietly expired in December 2009, but the two sides have been discussing a replacement since at least April 2009. START originally limited nuclear stockpiles to 6,000 weapons each. Subsequent amendments, most recently in July, brought the limits down to roughly 2,000 each.

Obama spent Wednesday briefing Democratic Sen. John Kerry, chairman of the Senate Foreign Relations Committee, and Sen. Richard Lugar, the committee's ranking Republican. Both would play major roles in Senate ratification of the emerging treaty.

A formal, 20-page protocol document is expected within days, followed by an "annex" of amendments before the unveiling in Prague.

Negotiations are centred on disputes over verification measures and Russia's objection to U.S. missile defence plans for Europe.

Russian negotiators have balked at including some intrusive weapons verification measures in the new treaty. The Obama administration has warned that without these, Senate ratification could prove difficult.

Any agreement would need to be ratified by the legislatures of both countries and still would leave each with a large number of nuclear weapons, both deployed and stockpiled.