Russia's lower house of parliament Friday gave initial backing to a historic treaty with the United States to slash the nuclear arsenals of the Cold War foes but warned final ratification would drag into next year.

The State Duma lower house of parliament voted with 350 in favour and 58 against for the new Strategic Arms Reduction Treaty (START) signed by Russian President Dmitry Medvedev and US President Barack Obama on April 8.

Yet hopes ratification could be wrapped up by the end of the year after the US Senate's approval Wednesday were dashed when top Russian officials voiced unease at additions made by US senators to their own ratification resolution.

The head of Russia's foreign affairs committee Konstantin Kosachev said the non-binding US attachments meant that a second of the three required votes on the bill would not be held until "January at the earliest".

Foreign Minister Sergei Lavrov sounded an optimistic note by observing that "common sense" had prevailed because neither side had introduced changes that undermined the essence of the treaty.

But he stressed that Russia was "absolutely not in agreement" with a Senate amendment insisting on the United States' right to build a missile defence system in Europe and convert strategic offensive weapons into defensive ones.

"This is an arbitrary interpretation of the principles of international law. The agreement, like any other, is a single whole," he said.

The new START treaty restricts the former nuclear rivals to a maximum of 1,550 deployed warheads each -- a cut of about 30 percent from a limit set in 2002 -- and 800 launchers and bombers.

The cuts focus exclusively on "strategic" nuclear weapons that are designed to destroy large populations or damage the enemy's ability to wage war.

The United States has a vast superiority in these weapons over Russia -- which enjoys an advantage in "tactical" weapons used in smaller campaigns -- a point stressed repeatedly by Defence Minister Anatoly Serdyukov during the brief Duma debate.

"We will not have to make any cuts to our strategic offensive weapons," the defence minister told sceptical Communist lawmakers who opposed the bill.

"These will be removed from service only when the time comes to decommission them."

But Russia is deeply concerned that the proposed US defence shield may one day be turned around to fire warheads at Russia.

Lawmakers now have until January to introduce their own counter-amendments to those adopted in Washington -- with Serdyukov urging deputies to assert their own interpretation on the missile shield.

"We think it essential that the State Duma adopt a declaration confirming the importance of the link between strategic offensive and strategic defensive arms," Serdyukov said.

The Duma's first reading vote only signifies approval of the original form of the treaty signed by the presidents in Prague.

But US senators argue that the treaty does nothing to prevent the United States from deploying a missile shield that Russia also fears may one day be expanded to hurt its own nuclear capabilities.

"These issues have to be studied very carefully," the Duma foreign affairs committee chief Kosachev warned before the vote. "And that takes time."

Russia's two houses of parliament are dominated by pro-Kremlin lawmakers and there is almost no doubt that they will eventually approve the pact.

Medvedev has called on lawmakers to pass the measure and described the Senate's ratification as a "historic event for both countries and for US-Russia relations."

The Kremlin chief also hailed Obama as a man who keeps his promises and urged him to relax over the holidays.

"He is a man who fulfils his promises. I wish my colleague a good rest, he did a quality job," Medvedev said in a live end-of-year television interview.