The five-candidate special election on April 20 to fill a vacant seat on the Roseville City Council seems made to order for the voting method known as "instant runoff."

Instead of voting for one candidate, "instant runoff" voters could rank the candidates in order of preference. Ballots would be counted by first- place choices. If no candidate received a majority of first-place votes, the second choices of the candidate with the fewest first-place votes would be tallied. That sorting process would continue until one candidate had enough first and second-place votes to exceed 50 percent.

That's the beauty part of this vote-by-number method. In contests with more than two candidates, it better reflects the will of the people, by assuring that the winner captures a majority of first- and second-place votes. The darling of a minority faction, detested by the majority, could not win.

A runoff election might produce the same result, but with a delay of several weeks, and, in Roseville, at the $18,000 cost of opening the polls for a second time.

All five candidates in Roseville have said they favor settling their contest with an instant runoff election. So does the City Council, which in January unanimously asked the Legislature for permission to give this voting method a try.

The Minnesota Senate said yes on Feb. 23 -- but its 38-26 vote suggests that the bill faces trouble in the Republican-controlled House. All the no votes in the Senate were cast by Republicans. That party obviously has enjoyed an advantage in the plurality-rule elections of recent years. The multicandidate races legislators know best have been multiparty contests, with Green and Independence Party candidates tending to take votes away from DFLers and clearing the way for GOP victories. Republicans don't want to ask Green and IP voters for their second choices, let alone count them.

Such self-interested reasoning should not stand in the way of Roseville's request. City elections in Minnesota are nonpartisan. The bill before the House is specific to one election in one community, and gives that community's government the chance to choose which voting method to employ. It requires no costly change in voting equipment, since the number of votes likely to be cast in the election is small enough to allow for hand counting of second choices.

Rather than seeing Roseville's instant runoff request as a politically hazardous precedent, House members of both parties should regard it as a low-cost, limited, locally controlled test of a new way to determine the will of the people. Democracy occasionally needs laboratories, and Roseville would make a good one on April 20.