If U.S. military leaders say that maintaining the flow of Russian-made weaponry into Afghanistan will keep the war effort on track, "I defer to the Defense Department [on the issue]," Lieberman told reporters Wednesday.
His comments come a day after Maj. Gen. William Crosby told House defense lawmakers that the DOD had no plans to cut ties with Russian defense firm Rosoboronexport.
The Russian company is under DOD contract to supply Mi-17 helicopters to Afghan security forces.
A bipartisan group of 17 senators sent a letter to Defense Secretary Leon Panetta on March 12, urging the Pentagon to end its relationship with the Russian firm.
Defense Department officials claim that cutting off Rosoboronexport and losing those supplies of Mi-17s would significantly delay U.S-led training of Afghan forces.
American and coalition advisers would have to start from scratch teaching the Afghan forces, many of whom "can't read or write" how to use helicopters other than the Mi-17 under battlefield conditions, Crosby said Tuesday.
Boosting the capability of the Afghan military is key to the White House's plan to have all American troops out of Afghanistan by 2014.
Lieberman acknowledged the difficult position the Pentagon was in, regarding its relationship with Rosoboronexport and the company's alleged role in Syria.
The Connecticut lawmaker was one of five senators, including co-sponsor Sen. John McCain (R-Ariz.), who introduced a new resolution on Wednesday pressing for U.S. military involvement in the country.
Russia has exercised "unacceptable international behavior" in its dealings with the Assad regime, McCain said during a Wednesday briefing on Capitol Hill.
Aside from selling weapons to Syrian government forces, recent news reports claim Russian special forces have been sent to Syria to help put down the rebel opposition.
However, if the Pentagon must keep working with Russian industry to ensure U.S. and Afghan soldiers have what they need, then those ties must continue, according to Lieberman.