PENNSYLVANIANS are blessed - or is it cursed? - with an interesting Senate race: In next week's primary, five- term incumbent Republican-turned-Democrat Arlen Specter faces off against the more liberal challenger, retired Navy admiral Joe Sestak; the winner will likely take on Republican conservative Pat Toomey in the fall.

This race and its eventual outcome could be read as a microcosm of the American political landscape. But will it represent a dramatic turning of the political tide (Scott Brown's win in Massachusetts) . . . or a prelude to extremes settling down to moderate practicality (Scott Brown's vote for a Democratic jobs bill)?

Whatever happens in November, Pennsylvania's Senate race will no doubt be seen as a bellwether for the nation, embodying a shift rightward, or a more moderate staying-of-the-course.

As trends go, we prefer the latter. But that's only a small part of why our endorsement goes to Arlen Specter. After all, the last thing you can accuse Arlen Specter of is "staying the course."

He helped John Roberts get to the Supreme Court, but now says he regrets taking Roberts at his word during confirmation hearings. He didn't support the public option but then changed his mind. And then there's that party shift: He said he felt abandoned by an increasingly right-wing Republican Party; last week, he said he might have helped the country more if he had stayed Republican and sowed seeds of moderation within the party.

In a less-seasoned player, this would be sign of flip-flopping. But Specter is savvy enough to suggest he comes by these changes honestly, as part of a process of finding the truth in issues that resist easy answers. He has been smart and tough enough to survive - and thrive - while resisting easy categorization.

By endorsing Specter, we endorse a man who has done well by his state, and commands authority and respect in Washington that ensures he can still get things done for the state and the region. His introduction of a bill to make witness intimidation a federal crime is a direct response to the problems we are having here in the city. He has also called on the federal marshals to help track down fugitives, another local epidemic.

Specter's opponent is a worthy opponent. Sestak unseated incumbent Curt Weldon in the 2006 congressional race, surprising many. His short tenure in Congress is no match for Specter's long and admirable record.

With Democrats at risk of losing the majority in the Senate, they need the strongest candidate possible - one who can stand firm against shifting winds and continue to set the agenda.

For that reason, Arlen Specter is our choice in this race. *