WASHINGTON - US Senator Robert Menendez, the chairman of the influential Senate Foreign Relations Committee, introduced a bill on Monday that would provide weapons to some vetted groups of Syrian rebels.Menendez, a Democrat, was one of a few senators pushing the White House to provide for lethal aid to some of the rebels fighting the government of Syrian President Bashar Assad even before reports that chemical weapons had been used in the conflict.The bill would have to get through the committee and be approved by both the Senate and House of Representatives, and signed by US President Barack Obama before becoming law.