Sen. John McCain (R-Ariz.) got an answer from Sen. Barack Obama (D-Ill.) Tuesday on his proposal for 10 town hall-style debates: Not going to happen. That’s too bad — and, the fewer there are, the more Obama should suffer for it politically.

[IMGCAP(1)]The town halls not only would give ordinary citizens a chance to ask the candidates some pointed questions (see suggestions below), but — because they would be nationally televised — they would let voters nationwide see how the candidates handle challenges from across the political spectrum.

When Obama was debating Sen. Hillary Rodham Clinton (D-NY) and — in the distant past — when McCain debated his GOP rivals, the Democrats rarely got tough questions premised from the right, or the Republicans, from the left.

McCain has challenged Obama to 10 joint appearances to take place before the national conventions. Obviously, McCain thinks they’re to his advantage because Obama is such a better orator and McCain performs well in informal settings.

Moreover, McCain — with less money to spend than Obama — wants the free national exposure that the town halls would provide. Obama is ahead in the polls and probably doesn’t want to risk his advantage on possibly risky joint appearances.

So, on Tuesday, Obama told reporters, “You know what we’ve said is we are happy to do more than the three typical presidential debates in the fall … We hope to have negotiations soon.”

He added, “It’s not realistic for us to do 10 … It will probably be somewhat fewer than 10 but more than the three that have been already agreed to, and we’ll probably propose a mix of formats.”

That’s a far cry from the ideal — 10 or more free-wheeling, longish (say, 90 minutes) exchanges centered on a specific topic area but with time left for random (say, political) inquiries. The questioners could be a mix of ordinary citizens and policy experts, maybe with a media person occasionally thrown in.

The ideal would be an exchange very soon on Topic A — gasoline prices, energy policy and environmental policy. Sample question: Senators, you both complain about high gasoline prices but also favor a cap-and-trade system to control global warming. That surely will raise energy prices — in fact, it’s meant to. How does that square?

Also, you both oppose drilling in the Arctic National Wildlife Refuge and off-shore, yet you talk about making the U.S. less dependent on foreign sources. How can you do that — and don’t talk about ‘alternatives’ like wind and solar, which can’t replace oil for decades?

If gas prices are Topic A, then the economy and jobs are Topic A1/2 and deserve the second exchange — also soon. McCain needs to be asked: You favor extending all the Bush tax cuts — but they haven’t raised incomes for the average American. Why do you think they would in the next four years?

And, Sen. Obama, all your promises — middle-class tax cuts, infrastructure, education, health care and energy investment — will cost how much? Three trillion dollars over 10 years, as Sen. McCain charges? How are you going to pay for that with just tax increases on the wealthy, estimated to raise $1.5 trillion?

Both candidates also need to be asked: Just what are you going to do to prevent meltdowns in the housing and financial markets — and why are your solutions better than his?

There ought to be two or more debates on foreign policy — one on Iraq, one or more on the rest of the world. Question for Obama: Suppose the U.S. had followed your policy and hadn’t done the surge in Iraq — wouldn’t al-Qaida now be in charge of Sunni areas, radical militias of Shiite areas and wouldn’t the U.S. have suffered a strategic defeat it might now avoid? That is, wasn’t Sen. McCain right?

To both candidates: If diplomacy can’t stop Iran’s nuclear program, are you going to bomb?

There ought to be separate town halls on entitlements, education, health care and trade. So, some more questions: Sen. Obama, even AARP advocates some shaving back of retirement benefits to prevent Social Security and Medicare from going broke. Why don’t you?

Sen. McCain, independent analysts say that your health care proposal — detaching insurance from the workplace — will make insurance unaffordable for older and sicker workers, and those whose kids may have pre-existing conditions. What about that?

Both of you: A third of ninth graders won’t finish high school — 50 percent for minority kids. Where is the dropout crisis on your priority list? Come to think of it, both of you have put a lot of proposals out there — what will you tackle first, second and third?

So many questions, so little time. If Obama really means to change the political landscape, he ought to agree to lots of open exchanges with McCain. And if he won’t, the media should ask, why not?