A bipartisan group of 12 senators unveiled legislation Wednesday that would reject a proposed 50 percent congressional pay raise, and roll back the increase if the House lets it become law.

The rollback proposal is designed to give Senate pay-raise opponents a better weapon than a simple resolution to turn down the increase. It could keep the issue alive even if the raise goes into effect.Senators are expected to overwhelmingly reject the pay raise, while at the same time knowing that a House vote appears unlikely. Unless both chambers reject the pay plan recommended by former President Reagan, the raise would become law automatically on Feb. 8.

Reagan, following the advice of a commission, recommended that congressional salaries rise from $89,500 to $135,000 for rank-and-file lawmakers.

The recommendation would allow the House speaker to receive $175,000 instead of $115,000; and would pay $155,000 to the president pro tempore of the Senate and the majority and minority leaders of each house - all of whom now earn $99,500.

Reagan also recommended 50 percent increases for top political appointees in the executive branch and for judges.

Sen. Larry Pressler, R-S.D., a main sponsor of the new legislation, said the rollback was the key provision. If the Senate approves the legislation and sends it to the House, House opponents of the raise could keep trying to tack it on to other bills after Feb. 8.

The legislation also would require a vote on all future pay raises.

Senate sponsors accused the House leadership of trying to duck a vote. Speaker Jim Wright, D-Texas, has been non-committal, while Senate Majority Leader George J. Mitchell, D-Maine, has promised a Senate vote.

"It's ridiculous not to have a vote on the pay raise," Sen. Charles E. Grassley, R-Iowa, told reporters. "Not only is the amount outlandish, but it sets a pretty bad example. The public hates the pay increase and the way it's approved."

Any rollback also would affect 50 percent raises for top executive branch officials, which also were part of Reagan's recommendation.

The Senate sponsors of the legislation are Sens. Pressler; Grassley; Harry Reid, D-Nev.; Jesse Helms, R-N.C.; John McCain, R-Ariz.; Dennis DeConcini, D-Ariz.; Paul Simon, D-Ill.; Gordon Humphrey, R-N.H.; David Boren, D-Okla.; Quentin Burdick, D-N.D.; Strom Thurmond, R-S.C. and Howell Heflin, R-Ala.