Washington (CNN) -- U.S. and Russian teams negotiating a new arms control agreement to replace the 1991 START treaty hope to wrap up a deal by early April, nearly a year after they began.
A U.S. official with knowledge of the negotiations but not authorized to speak on the record told CNN the talks on the treaty, which expired December 5, 2009, have been "very tough" but said, "I think we can do it."
The biggest issue to resolve is verification, including on-site inspection of missiles that carry nuclear warheads, this official said, adding, "There are still some niggling technical details."
Negotiators worked out "innovative" ways of verifying each side's arsenal, the official said. When negotiations began in April 2009, Russia wanted a "minimalist" approach to verification and the United States wanted a "solid, effective regime," the official said.
"We pushed them constantly for more," the official said. "We always knew we would need a bridge to the next phase of deep reductions."
Verification will be a top issue politically as both the U.S. Senate and the Russian parliament, will have to ratify the new agreement.
"We will see a strong verification process," the official said. '"We're developing a lot of new ways to bump up the verification regime."
As the arms talks have continued, the U.S. team has grown from 10 to 12 people to a total of 35, which now includes lawyers and specialized linguists who must certify that the English and Russian language texts are precisely equal.
The Russian team includes representatives from the Ministry of Defense and the FSB, successor agency to the KGB. Many of them are new to negotiating but "know the innards of the Russian strategic rocket forces" and are very good, the official said.
Russian President Dimitry Medvedev "is very serious about this and about the caliber of the people," the official said.
Both sides are aware that times have changed and the Cold War is over. The U.S. official said one inspector on the Russian team pointed out that once-sensitive information, like the location of Russia's strategic forces, is available to anyone by doing a simple Web search.
A key point of the agreement already has been worked out: reducing the number of allowable deployed strategic warheads on each side. The United States currently has approximately 2,200 strategic deployed warheads; Russia has an estimated 2,500. Under the new agreement, each side would be allowed between 1,500 and 1,675 nuclear warheads.
The treaty also limits the number of "delivery vehicles" -- the strategic bombers and missiles that carry those warheads -- to between 500 and 1,100 for each side. The current limit is 1,600 but the United States actually has 900 delivery vehicles. Russia has an estimated 600. For the American side, President Obama will have the final word on the precise numbers within those parameters.
The Bush administration downplayed the need for a formal arms control agreement and the U.S. official said, "The amount of disconnectedness" between the two sides "at the end of the last administration was just incredible."
The talks, however, have been a "revelation" and a "surprise," the officials said, setting the stage for even further arms reductions. This will help, the official said, after the replacement agreement to START is finished, when negotiators will tackle more thorny issues like nondeployed warheads kept in storage, tactical nuclear weapons and further cuts in missiles and launch vehicles.