Washington (CNN) -- The United States and Russia have reached "the most comprehensive arms control agreement in nearly two decades," President Obama said Friday.

The agreement cuts by about one-third "the nuclear weapons that the United States and Russia will deploy," the president said.

The new Strategic Arms Reduction Treaty (START) will last 10 years, and builds on the previous agreement that expired in December.

"It significantly reduces missiles and launchers," Obama told reporters at the White House. "It puts in place a strong and effective verification regime. And it maintains the flexibility that we need to protect and advance our national security, and to guarantee our unwavering commitment to the security of our allies."

Obama and Russian President Dmitry Medvedev will sign the agreement April 8 in Prague, Czech Republic, Obama said, calling arms control "one of his administration's top national security priorities."

Information released by the White House says the new treaty limits both nations to "significantly fewer strategic arms within seven years" of its signing. One of the limits: 1,550 warheads. "Warheads on deployed ICBMs (Intercontinental ballistic missiles) and deployed SLBMs (submarine-launched ballistic missiles) count toward this limit and each deployed heavy bomber equipped for nuclear armaments counts as one warhead toward this limit," the White House said. There are also limits on launchers.

The treaty lays out a "verification regime" that includes on-site inspections, data exchanges and notifications, the White House said.

"The Treaty does not contain any constraints on testing, development or deployment of current or planned U.S. missile defense programs or current or planned United States long-range conventional strike capabilities," the White House said.

Obama said the agreement is part of the U.S. effort to "reset" the U.S. relationship with Russia.

"With this agreement, the United States and Russia -- the two largest nuclear powers in the world -- also send a clear signal that we intend to lead," the president said. "By upholding our own commitments under the Nuclear Non-Proliferation Treaty, we strengthen our global efforts to stop the spread of these weapons, and to ensure that other nations meet their own responsibilities."

President Obama, Secretary of State Hillary Clinton, and Defense Secretary Robert Gates said the changes will not hamper the U.S. ability to protect itself and its allies.

Negotiators have been working since April 2009 to wrap up the "follow-on" to the 1991 agreement. Talks were difficult, with disagreements over verification, including on-site inspection of missiles that carry nuclear warheads.

A U.S. official with knowledge of the talks earlier told CNN that negotiators had found "innovative" ways to verify what each side has. Verification will be a top issue politically because the U.S. Senate and the Russian parliament will each have to ratify any agreement.

Russian officials at one point objected to the Obama administration's plans to build a missile-defense system in Eastern Europe. Specifically, they were angered by news leaks from Romania that it had agreed to allow missile interceptors to be installed in that country.

The issue, according to arms control experts, was resolved by including non-binding language in the START treaty's preamble stating that there is a relationship between offensive and defensive weapons; however, the treaty itself deals only with limits on offensive weapons systems. This resolution could help placate U.S. critics who want no link in the treaty between offensive and defensive weapons, arguing that it might be used to try to limit a U.S. missile-defense plan.

The new START would be the first treaty related to arms control since the end of the Cold War, experts have said, setting the stage for further arms reductions that will tackle thorny issues like what to do with non-deployed warheads that are kept in storage, tactical nuclear weapons and further cuts in missiles and launch vehicles.