This month’s dismissal of Carol Bartz as CEO of Yahoo, and the concomitant appointment of finance chief Tim Morse as her interim replacement, bring a new spotlight to an old question: Are CFOs qualified to be chief executives, even for a short while?

As to permanent positions, companies generally are skeptical. Only 7.7% of the CEOs of the 669 companies in the Fortune 500 and the S&P 500 were CFOs in their immediately previous roles, according to the just-released “Volatility Report 2011” from executive-recruiting firm Crist|Kolder. One-fourth do have some CFO experience, but just 36.5% have any kind of financial-executive experience.

Data is harder to come by for interim CEO appointments, including how often the CFO is the choice over presidents and chief operating officers. But when CFOs do get to the top slot on a temporary basis, not many stay on in the role permanently. Tom Kolder, president of Crist|Kolder, estimates that no more than 20% do so. And if they don’t serve at least nine months in the role, they realistically have no chance to stick at the top slot, he says.

A contributing factor may be that most CFOs aren’t exactly campaigning to be a chief executive. “It’s fairly easy to position CFOs as interim, because they typically don’t want the job,” says Mike Lehman, the longtime finance chief for Sun Microsystems, who now fills that role at Palo Alto Networks.

Lehman’s perspective on the matter is fresh. After Palo Alto’s CEO departed last December, Lehman filled in for him through August as part of a three-person “Office of the CEO.” Like many of his counterparts, he says he prefers being the chief executive’s right-hand man, acting as a business partner, and working with the board of directors. “I have worked with and mentored a lot of CFOs, and many of them feel the same way,” says Lehman.

When John Leahy, currently CFO at iRobot, was tapped as interim CEO at Keane in 2006, the scale of the work in front of him was immense. “It was very stressful, and probably not [something] I’d want to go through again,” he says.

Keane’s CEO had left on short notice, and almost concurrently with that, the board launched an exploration of opportunities to sell the company. Overnight Leahy had to not only continue running finance but also oversee an intense, confidential selling process. “I really had my hands full,” he says. “And it helped make it clear to me that finance is what I really enjoy doing. Being a CEO involves a lot more time, and you’re doing a lot of it out in the public domain, with customers or trade groups. It’s not what I would prefer to do.”

Still, Leahy says, it was an incredible learning experience. He got to see the company through a different and much wider lens. He had to rally the management team, become more involved cross-organizationally, act as chief communicator to 10,000 employees, and, because he was in the position for nine months, make some difficult organizational moves as the company sale approached.

What saved him, he says, was that he had strong people in the controller, corporate finance director, and CIO roles, so he was able to delegate heavily.

Certainly, there are some CFOs who do have a taste for running a company. Stuart Jones, currently managing partner of Professional Management Co., a consulting firm that provides interim management and financial consulting services, says he had an eye on being a CEO ever since he majored in accounting at the University of Virginia.

“There are many pure finance people, especially CPAs, who like to be the quiet number two,” says Jones. “I’m just the opposite. I’ve always aspired to be the CEO, and used CFO jobs I had as a springboard to get there.”

But he didn’t, like a majority of CFOs, go on to public accounting himself. Rather, he got an MBA at the University of Illinois and went to work for Ford Motor as a financial analyst. At Ford, he says, certified public accountants kept the books, while MBAs performed financial analysis before moving into general management. He went on to be CFO of a small private company, CFO of a Nasdaq company, and international controller for a Fortune 500 company. He was also CFO of a group of divisions at another public company, where he took over one of the divisions as interim CEO. And he took on a role as de facto CEO of a failing real estate investment trust whose liquidation he oversaw.

“I would have preferred to have had more CEO time and less CFO time,” says Jones. “I majored in accounting because I wanted to understand the numbers thoroughly, but to me they were a tool rather than becoming all that I did.”