We have barely four months-not the nine that some seem to think-to start and finish complex arms-control negotiations in an atmosphere of tense relations between Moscow and Washington. President Obama will have to address this task with a sense of urgency and with great focus.

If we do not move quickly on talks to renew the Strategic Arms Reduction Treaty (START), the foundation of the U.S.-Russian strategic relationship is at risk of collapsing. The START verification regime is a proven system of on-site inspections and detailed data disclosure that provides each side with confidence that the other is living up to its obligations. Without it, the rug is ripped out from under the 2003 Moscow Treaty-which calls for dramatic reductions in Russian and American nuclear arsenals down to seventeen hundred warheads each-because it has no verification provisions of its own.

The Bush administration regrettably did not make progress in the talks, leaving President Obama's team with little time. The START treaty expires on December 5, but this is misleading. If the Senate is to ratify a new treaty before then, it will have to be submitted to Congress by early fall, to allow for hearings, debate and a floor vote. (The Moscow Treaty itself, only three pages long, took nine months from submission to ratification.) This, in turn, means that the treaty will have to be signed by both sides no later than early August to clear the necessary bureaucratic processing. That's the real deadline.

The Senate needs to confirm in the next few days President Obama's nominee to be assistant secretary of state for verification, compliance and implementation, Rose Gottemoeller, who would be in charge of the negotiations. She was approved by the Senate Foreign Relations Committee on March 31.

President Obama must carefully set priorities and pick a limited set of U.S. goals in the negotiations. The primary goal should be to solidify the START verification regime and to maintain legally binding commitments on both sides in the Moscow Treaty. To lead is to choose, and the president and Secretary of State Clinton must resist calls to load the negotiations agenda with objectives that, while desirable, would slow down the talks and threaten the tight timetable.

Some outsiders have urged the administration to aim high by seeking to negotiate even lower strategic-nuclear-weapons levels, to devise a structure to address tactical nuclear weapons, establish a framework of cooperation-rather than confrontation-over missile defense, and break the current stalemate over reductions in conventional forces in Europe. These are worthy goals, but first things first: let's renew the central arms-control agreement between our two countries. Then we'll be in a better position to tackle these more complicated issues.

Reaching common ground on START will represent more than an essential step toward better bilateral relations. It is also crucial in helping Moscow and Washington address one of the biggest global threats we face-the rising danger of nuclear-weapons proliferation. The Nuclear Nonproliferation Treaty (NPT) is under stress from the nuclear-weapons programs in Iran and North Korea and the concerns of neighboring countries. At the same time, the spread of nuclear power for electricity generation is raising the risks that terrorists or rogue states could get their hands on material for an atomic weapon.

The NPT Review Conference next spring, to be attended by more than one hundred developed and developing nations, will be a crucial forum to start repairing the cracks in the nonproliferation regime. But restive non-weapons states have grown increasingly loud in their complaints that Russia and the United States have not done enough to fulfill their treaty obligations.

As part of a larger strategy to address these concerns and enhance the credibility of the NPT system, Washington and Moscow must not show up for the conference empty-handed. That means the signing and ratification of a new START treaty. With the reality of the congressional and bureaucratic timetables I have outlined, we have no time to waste.

Richard G. Lugar is the ranking member on the Senate Foreign Relations Committee.