IF YOU HAD a few minutes with Republican presidential candidate John McCain, what would you ask him?

I confronted this dilemma when his campaign offered me half an hour with him yesterday on his campaign bus, "The Straight Talk Express," along with four other print reporters - "just the four of you and him having a conversation," campaign spokesman Paul Lindsay said.

Since the candidate's off-the-cuff charm is seen as perhaps his greatest asset, serving a dollop to local reporters is worth a bit of his time. And I mean just a bit.

Simple arithmetic told me that my share of the conversation would be about six minutes, so I decided to bore in on one issue. It had to do with the subprime mortgage disaster, and whether a key member of the McCain team had in fact paved the way for this mess.

So as we settled into our seats around a table with McCain, I asked about the fact that his campaign co-chair and economic adviser, former Texas Sen. Phil Gramm, was co-sponsor of the 1999 law that allowed commercial banks to get into investment banking. And the fact that Gramm was a prime architect of a 2000 bill that kept regulators' hands off of "credit default swaps," an exotic financial tool which helped enable the bundling and selling of crappy subprime mortgages to investors.

Michael Greenberger, who headed the Commodity Futures Trading Commission's division of trading and markets in the late '90s, said that the unregulated swaps "have been at the heart of the subprime meltdown."

Liberal writers raised this issue a month ago, along with the fact that Gramm had lobbied the federal government for the Swiss bank UBS - a key player in the uproar over these mortgage schemes - as recently as early this year.

I opened the subject with McCain by noting that on the issue of campaign finance, he'd seen a need for stronger government rules to regulate private conduct. I asked if the kind of aggressive deregulation that Gramm has championed had laid the foundation for a financial nightmare that's affected the entire economy.

McCain listened while munching on a chocolate doughnut and sipping a tall cappuccino, and then came back hard.

He noted accurately that the bills that Gramm had favored were supported by a lot of people, including Democrats and financial guru Alan Greenspan.

He cited Gramm's crusades against excessive government spending, and said that he was "one of the smartest people in the world on economics." And he said that Gramm and others thought that they were doing the right thing in the 2000 legislation.

But that's just the point.

Nobody thought that they were setting up a cataclysmic collapse in the nation's financial sector, but when you're restricting public oversight of private markets, you'd better give some serious thought to the downside.

Since McCain has admitted that the economy isn't his strong suit, I'd like to know that he's thinking these issues through, and not adopting a laissez-faire, supply-side approach uncritically.

I noted that the housing crisis plan on McCain's Web site proposes help for struggling homeowners and a task force to investigate criminal wrongdoing in the mortgage industry, but had nothing to say about regulatory reform.

McCain said that he supports "a lot more transparency and oversight" in financial markets. When I pressed for specifics, he referred me to plans advanced by Treasury Secretary Henry Paulson.

It wasn't an entirely satisfying exchange, but I could see why McCain likes the unscripted give-and-take. Even when he was thin on specifics, he spoke with clarity and conviction, and graciously acknowledged the viewpoints of others.

McCain called opponent Barack Obama a patriot and "a great American success story," and said that he accepted Obama's rejection of controversial comments about McCain's military record by retired Gen. Wesley Clark.

But he also took measured but effective shots at Obama when the conversation lent an opening.

At an afternoon town meeting at a Bucks County sheet-metal fabricating plant, McCain took a wide range of questions and spoke effectively about pork-barrel spending, energy independence and winning in Iraq.

He said that he's the underdog in Pennsylvania, but that he plans to ride his bus all over the state - and win it in November. *