The Senate voted Tuesday to limit debate on the New Strategic Arms Reduction Treaty (START), paving the way for final ratification of the arms-control pact as key Republicans defied their party leadership and announced support for the accord.

The move to invoke cloture passed by a 67-28 vote after several days of debate and unsuccessful Republican attempts to add amendments to the U.S.-Russia arms agreement.

The Senate could take a final vote to formally ratify the treaty as early as Wednesday...