Rep. Mike Castle (R., Del.) turns 70 next month, and he's facing a tough career decision.

"They've asked me to run for the Senate as a Republican. I don't know if I'm going to do that," business-friendly Castle told a crowd of financial planners at Cira Centre in Philadelphia yesterday.

If he takes Vice President Biden's old seat next fall, the former governor, who's kept his House seat since 1992 by mostly landslide margins, would break the Democratic monopoly on the tristate area's Senate delegation. (So would a loss by Arlen Specter or whomever his new party ends up running in Pennsylvania.)

Castle knows his likely opponent would be Biden's son Beau, Delaware's attorney general, now serving as a National Guard lawyer in Iraq.

The Biden dynasty draws national money. Meanwhile, says Castle, "my wife talks about beaches in Florida. I don't know if I want to run for the House again, let alone for the four years of Biden's term."

But Castle's the last proven vote-getter the Republicans have in the First State. If he steps down, Democrats could take both Senate and House posts. "That's the quandary."

Face facts

How do you pass the torch if there's no one behind you?

"I'm worried about the Republican Party," Castle said. "The Republican message is getting a little old. We're still talking about Ronald Reagan," who was president "before some of the voters were born."

Unpopular stands on "social issues" may have hurt the party. But "what hurt the most was the eight years of President Bush in which the very issues we're talking about today were not addressed. That has been a very strong negative for the Republican Party.

"My vision for the Republican Party is a presidential candidate who can be a good leader. . . . I know it's not Sarah Palin or Newt Gingrich or Dick Cheney."

The Republicans need "a manager." Maybe Minnesota Gov. "Tim Pawlenty, or Florida Gov. Charles Crist . . . someone who can say, 'Here's what we should be doing for Social Security or health care.' " And get back on the national agenda.

Smart or right?

As governor, Castle helped lure the nation's credit-card banks to Delaware, and he's been a bankers' ally in Congress.

He doesn't brag about it. "I'm a so-called senior member of the Financial Services Committee. That doesn't mean I know what I'm talking about."

But then again, "I listen to Mr. Bernanke talking about the future of the country. I scratch my head and wonder if he knows what he's talking about.

"Geithner . . . needs a heck of a lot more help. My sense is President Obama doesn't have a lot of financial background. And, I'm from Delaware, and I know Joe Biden has no financial background . . .

"Barney Frank," the Democratic chairman of the House banking committee, "sort of does know what he's talking about. He's also a lot smarter than everybody else and he's extraordinarily strong. That makes me nervous."

Obama adviser and ex-Treasury Secretary "Larry Summers is another extraordinarily strong individual. . . . He's very smart. But is he doing the right thing?"

It's your money

"What we do in Congress is very simple," Castle said. "We borrow the money. We pay the money. We add it to our debt total, which is $11 trillion. . . . How will it be paid? Down the road. By you." And probably after an ugly price inflation.

He calls Obama's financial-regulation proposals "confusing, but a start." The plan to force lenders to hold more capital "would solve a lot of our problems."

He's worried about the Federal Reserve doing too much in secret. Castle and Sen. Susan Collins of Maine sponsored Republican proposals to put an independent board in charge of weighing "systemic risk," instead of giving that power to the Fed, as Obama wants.

But Castle's been in the minority long enough to know "the administration usually gets what it wants."

He told me he'll decide about a Senate run - or retirement - by the end of summer.