How does one count some of the world's deadliest weapons? Should nuclear warheads be separated from the missiles that carry them? Should conventional warheads be subject to reduction targets?
Those questions - reminiscent of Cold War-era arms-control negotiations between the United States and the Soviet Union - are back on the global agenda as Washington and Moscow try to "reset the button" of their relations.
"Arms control is the area where the United States and Russia have the longest history of cooperation, and it is the easiest place to renew the bilateral relationship," wrote Andrew Kuchins of the Center for Strategic and International Studies and Anders Aslund of the Peterson Institute for International Economics in a new book on U.S.-Russia ties.
Even as Secretary of State Hillary Rodham Clinton and Russian Foreign Minister Sergey Lavrov agreed last week that arms control - in particular, completing a follow-on accord to the 1991 Strategic Arms Reduction Treaty (START) before it expires in December - will top their immediate agenda, fundamental differences between the two countries remain.
The counting rules regarding weapons reduction is an area of major disagreement, diplomats and analysts said. While the Americans count only "operationally deployed" warheads, the Russians insist on including all strategic weapons in the target numbers.
"A future agreement should be legally binding," Russian President Dmitry A. Medvedev wrote last week in a letter to the U.N. Conference on Disarmament that Mr. Lavrov read to the delegates.
"It is of no less importance that the instrument should be forward-looking and should limit not only warheads but also strategic delivery vehicles, i.e. intercontinental ballistic missiles, submarine-launched ballistic missiles and heavy bombers," Mr. Medvedev wrote.
Because both countries reached the levels required by START at the beginning of the decade, they set new requirements in the 2002 Strategic Offensive Reductions Treaty (SORT), also known as the Treaty of Moscow, which was negotiated by the Bush administration.
SORT required that both countries reduce their arsenals to levels of 1,700 to 2,200 warheads, and today they are at the higher end, said Daryl G. Kimball, executive director of the Arms Control Association (ACA).
An article last summer in Arms Control Today, a magazine published by the ACA, suggested that "the upper limit allowed for strategic nuclear forces would be 1,700 deployed warheads, to be achieved by the end of 2012."
The article was written by Rose Gottemoeller, former deputy undersecretary of energy for defense nuclear nonproliferation and, until recently, director of the Carnegie Moscow Center, and Alexei Arbatov, head of the Center for International Security at the Russian Academy of Sciences' Institute of International Economy and International Relationships.
Ms. Gottemoeller is expected to become assistant secretary of state for arms control, which would give her a major voice in U.S. policymaking.
"Russia could easily agree to a ceiling of 1,700 warheads, because it would help to save money by not having to extend the service life of some obsolete systems," the authors wrote. "It would also allow Russia to allocate more funding to a reasonable force modernization, including early-warning and command and control systems."
That target, however, may be more difficult for the U.S., especially if it includes conventional warheads, they wrote. Converting nuclear warheads into conventional ones, which Washington has favored, is unlikely to be accepted by Moscow as a reduction option.
Mr. Kimball said a START replacement could include different ways of achieving the necessary cuts, such as "downloading warheads" from delivery systems, reducing the number of those systems or limiting the number of warheads carried by each delivery vehicle. If the countries agree to keep some missiles, they will have to find a way to "assure the other side that the missiles are not armed," which could get complicated, he said.
In fact, verification is the other major problem as the U.S. and Russia prepare for negotiations. SORT does not include such provisions because the Bush administration stressed "transparency" more than verification. Such measures can be found in START, but experts deem many of them outdated.
So Ms. Gottemoeller and Mr. Arbatov proposed "an enhanced SORT."
"For the Russian side, the major goal would be to maintain a semblance of parity with the United States while addressing the basic problem with SORT, the lack of acceptable counting rules and corresponding verification procedures," they wrote.
"For the U.S. side, the major goal would be to maintain sufficient transparency with respect to Russian strategic nuclear forces while making sure that force cuts would not be too expensive for the United States," they added.
Although Mrs. Clinton said after a meeting with Mr. Lavrov in Geneva last week that there has been "some good preliminary work on START," Mr. Kimball said that "no decisions on the particulars of the U.S. negotiating position have been made."
An added bonus for resuming talks is that they could have outsize benefits for the U.S.-Russia relationship.
Gert Weisskirchen, a German parliamentarian and spokesman on foreign affairs for the Social Democrats, said Wednesday on a visit to Washington that it was important to bolster Mr. Medvedev at a time when he is trying to distinguish himself from hard-line Prime Minister Vladimir Putin and when Russia is "weak, not strong" because of plummeting oil prices.
"This could show Medvedev that the West is ready to open a new chapter and create a new framework for relations," Mr. Weisskirchen said.
President Obama and Mr. Medvedev are expected to meet on the sidelines of a global financial summit in London early next month. U.S. and Russian officials said the two leaders most likely will hold a summer summit, where they would review reports on the negotiations by their respective teams and agree on principles for the new treaty.
"We agreed to a work plan," Mrs. Clinton said in Geneva without elaborating. "We are going to create a very specific set of objectives and responsibilities. We hope to be in a position where we can present those to our two presidents before their meeting so that they can then agree upon the instructions that should be provided to our negotiators."