It's been a long time since Massachusetts voters faced an election for U.S. Senate without an incumbent on the ballot. In a one-party state like Massachusetts, the power of incumbency is all but absolute. Ted Kennedy served for 47 years, and Sen. John Kerry for 25 and counting.

It's been a long time since Massachusetts voters faced an election for U.S. Senate without an incumbent on the ballot. In a one-party state like Massachusetts, the power of incumbency is all but absolute. Ted Kennedy served for 47 years, and Sen. John Kerry for 25 and counting.

That's why the advantage of incumbency should be bestowed by the voters, not by the act of a governor filling a vacant Senate seat by appointment - whatever the governor's party affiliation. So we supported changing state law in 2004 to fill vacant seats by special election, and we take the same position now. Recent experience with gubernatorial Senate appointments in other states - notably Illinois and New York - have reinforced that conclusion.

Before his death last week, Sen. Kennedy pointed out the flaw in the law: Massachusetts would be short a senator during the five months between a seat becoming vacant and the special election, which could be critical at a time like this, when major issues are facing Congress.

Kennedy didn't suggest that the law be reversed, only that the governor be allowed to appoint an interim senator - one who promised not to be a candidate in the special election - to serve until a replacement was elected. Gov. Deval Patrick supports that change, and the state Legislature will take it up next week.

The strongest objection to amending the law seems to be that it is hypocritical of Democrats, who took the appointment power away when a Republican was governor, to give it back to a Democratic governor. Most Republicans, like most Democrats, prefer senators be elected rather than appointed, but contend that in 2004, the Democrats did the right thing for the wrong reason.

That argument ignores an important distinction. The previous law had provided for the governor to appoint a senator to serve out the remainder of the term. Under it, if Kerry had been elected president in 2004, Gov. Mitt Romney could have appointed a Republican to serve the remaining four years of Kerry's term. There's a big difference between appointing a place-holder for five months who cannot seek a full term and appointing a senator for four years, or, theoretically, as much as six years, who could hold the seat indefinitely.

The question of the five-month interregnum received little discussion in 2004, though Republican legislators proposed an interim appointment be included, an amendment rejected by Democrats. With the Senate at that point split down the middle, we don't doubt short-term politics was involved on both sides. Still, a five-month appointment should have been provided in the law then, and it should be now. To reject it now simply to punish Democrats for rejecting it then would be doing the wrong thing for the wrong reason.

No succession system will be perfect, and it might be most fair if the Legislature postponed changes in the law until there was no partisan interest in an immediate situation. But people don't repair tools they have no plans to use. The time to fix it is now, because the lack of full representation in the Senate is a problem now.

An explicit prohibition on the interim appointee running in the special election may not pass constitutional muster, but Patrick has promised to require such a pledge from whoever he appoints. We hope future governors would do the same in order to keep the special election playing field as level as possible. If a candidate breaks that pledge, the voters will be able to take that into account on Election Day.

True, letting a Democratic governor appoint an interim senator now gives a short-term advantage to Democrats, just as letting the seat sit vacant until the special election, now scheduled for Jan. 19, gives an advantage to opponents of Democratic initiatives. It's also true that a five-month campaign gives an advantage to candidates who are already well-known, with well-stocked federal campaign war chests.

But you can't take the politics out of politics. Kennedy's proposal is the fairest way to choose his successor without depriving the commonwealth of a voice in the Senate at a crucial time. Lawmakers should approve it, not out of partisan expediency, but because it makes sense.

MetroWest Daily News