Congress is lining up behind stretching the U.S. territorial limit to 12 miles out to sea and President Reagan is expected to make the change formal in the next few months, lawmakers said Friday.

The bill to accompany such a presidential proclamation was passed by the House on a voice vote Thursday and probably will be acted on by the Senate next week, said Rep. Norman Shumway, R-Calif.In addition to extending the U.S. territorial limit from the present three miles to 12 miles, the bill would extend to 24 miles the distance from shore the Coast Guard could board suspected drug-running ships of any nation.

"This legislation is very important for national security purposes . . . and also is very important to the drug interdiction effort of our Coast Guard," Rep. Mike Lowry, D-Wash., told the House.