Former President George H.W. Bush, who signed and won Senate approval of the original Start arms control treaty with the Soviet Union in 1991, endorsed the proposed follow-up treaty with Russia on Wednesday, lending another well-known Republican voice to the White House campaign for approval.

“I urge the United States Senate to ratify the Start treaty,” Mr. Bush said in a one-line statement that offered no elaboration. His spokesman, Jim Appleby, said by telephone that the former president would let his position stand at that and would not discuss whether the White House solicited the endorsement....