MOSCOW — The Russian government said Wednesday that it would not renew a hugely successful 20-year partnership with the United States to safeguard and dismantle nuclear and chemical weapons in the former Soviet Union when the program expires next spring, a potentially grave setback in the already fraying relationship between the former cold war enemies.

The Kremlin’s refusal to renew the Nunn-Lugar Cooperative Threat Reduction Program would put an end to a multibillion-dollar effort, financed largely by American taxpayers, that is widely credited with removing all nuclear weapons from the former Soviet republics of Ukraine, Kazakhstan and Belarus; deactivating more than 7,600 strategic nuclear warheads; and eliminating huge stockpiles of nuclear missiles and chemical weapons, as well as launchers and other equipment and military sites that supported unconventional weapons.

“The American side knows that we would not want a new extension,” a deputy foreign minister, Sergey Ryabkov, told the news agency Interfax. “This is not news.”

In a statement on its Web site, the Russian Foreign Ministry said that the Obama administration had proposed renewing the arrangement but that Washington was well aware of Russia’s opposition. “American partners know that their proposal is not consistent with our ideas about what forms and on what basis further cooperation should be built,” the statement said.

Russian officials, meanwhile, noted that their country’s financial situation is far improved from the days after the collapse of the Soviet Union, raising the possibility that Russia would be willing to continue initiatives started under the Nunn-Lugar agreement, but with its own financing and supervision. The Foreign Ministry, in its statement, noted that Russia has increased its budget allocation “in the field of disarmament.”

American officials, including one of the original architects of the program, Senator Richard G. Lugar, Republican of Indiana, have said they still have hope of reaching some form of new agreement with Russia.

But the prospects seem bleak.

President Vladimir V. Putin, while expressing a willingness to cooperate on nonproliferation issues, has said that a more pressing priority is to address Russia’s opposition to United States plans for a missile defense system based in Europe. President Obama has shown little willingness to make any concessions, other than to offer repeated reassurance that the system is not intended for use against Russia. And the Republican presidential nominee, Mitt Romney, seems even less likely to compromise on the missile defense issue.

The plan to end the Nunn-Lugar program appears to be the latest step by the Russian government in an expanding effort to curtail American-led initiatives, and especially the influence of American money, in various spheres of Russian public policy.

Last month, the Kremlin directed the United States Agency for International Development to halt all of its operations in Russia, which similarly entailed two decades of work, but in support of nonprofit groups like human rights advocates and civil society and public health programs.

The Russian government had made no secret of its unhappiness with some programs financed by the Agency for International Development, like Golos, the country’s only independent election-monitoring group, which helped expose fraud in disputed parliamentary voting last December.

Mr. Lugar, who is leaving the Senate at the end of this year, visited Moscow in August to begin pressing for renewal of the program and found Russian officials resistant. “The Russian government indicated a desire to make changes to the Nunn-Lugar Umbrella Agreement as opposed to simply extending it,” he said Wednesday. “At no time did officials indicate that, at this stage of negotiation, they were intent on ending it, only amending it.”

But Mr. Lugar, the senior Republican on the Foreign Relations Committee, lost a primary election this year in his bid for a seventh term, and he has acknowledged that there are few lawmakers who seem willing to carry on his efforts, which began in partnership with Senator Sam Nunn, Democrat of Georgia.

During his August visit to Moscow, Mr. Lugar said he hoped that the United States and Russia could use their past successes as a basis for expanding their efforts to reduce the threat of unconventional weapons in other countries. He raised the idea of trying to eliminate chemical weapons in Syria.

Russian officials, however, seem increasingly unwilling to let the United States set the agenda in global diplomacy — blocking demands, for example, for more aggressive intervention in Syria.

This article has been revised to reflect the following correction:

Correction: October 11, 2012

An earlier version of this article misspelled the surname of a deputy foreign minister. His name is Sergey Ryabkov, not Ruabkov.