Elevating the Veterans Administration to full Cabinet status will involve only changing a few signs outside the building, proponents said after the House voted overwhelming support of the change. Rep. Sonny Montgomery, D-Miss., said the cost of the change approved Thursday by the House will come to less than $1 million in 1989 and will give the nation's 27 million veterans direct access to the White House. The Congressional Budget Office has estimated that converting the VA into a Cabinet department would cost $33 million over five years. The House vote sent the compromise bill, making the VA the government's 14th Cabinet department, to the Senate, which was expected to add its approval. President Reagan backs the move, and it was his public announcement of support last summer that gave impetus to the legislation. House approval came on a voice vote, overriding objections from opponents who called the move an act of election-year pandering.