by Jill Dougherty

MOSCOW, Russia - Russian and U.S. nuclear negotiators have completed a joint statement on the framework for a new arms control agreement to replace the 1991 START I agreement which expires December 5.

A U.S. source close to the American side tells CNN that Presidents Barack Obama and Dmitry Medvedev will discuss the joint statement at their Monday meetings in Moscow and are expected to announce and sign it at their joint press conference Monday afternoon.

The agreement will set new limits on deployed nuclear warheads and on the delivery vehicles on which they are launched. The U.S. source refused to specify numbers but said they will be below the limits of 1,700 to 2,200 warheads set in the 2002 Moscow Treaty on Strategic Offensive Reductions. The joint statement also will set the number of delivery vehicles below 1,600 as designated in the START I agreement.

The joint statement is not legally-binding but politically instructs the Russian and U.S. negotiators to continue their work so that a formal agreement can be completed by the end of the year.

In a briefing Sunday night in Moscow, arms control specialist Gary Samore also refused to define the numerical limits in the joint statement but told reporters "There certainly won't be an agreement on the end deal... but I think you will see an announcement that indicates some progress toward reaching that objective."

After eight years in which the Bush administration dismissed the need for arms control agreements, the Obama administration has taken a diametrically opposed approach, making what experts call the "follow-on" agreement to the expiring START I treaty a priority.

In April during their meeting in London, Obama and Medvedev agreed to conclude the new agreement by the end of this year. The Brookings Institution's arms control expert Steven Pifer calls the new follow-on agreement "the first action in a step-by-step process of reducing their strategic arsenals with the ultimate goal of achieving a nuclear-free world."