CEOs for Paul Ryan? Not so fast.

August 14, 2012, 7:03 PM UTC

Paul Ryan

FORTUNE – CEOs have a big stake in the deficit debate. Some of the nation’s top business leaders have pressured Congress to tackle deficit problems in order to avoid large tax increases and spending cuts scheduled to take effect in January. The so-called fiscal cliff, they’ve argued, could send the economy back into a recession if lawmakers don’t act faster.

Now with Wisconsin Congressman Paul Ryan tapped as Republican presidential candidate Mitt Romney’s running mate, it would seem to bring executives a sigh of relief. After all, Ryan has been among the most assertive lawmakers preaching small government. But while having his name on the GOP ticket might help elevate the deficit as a main issue in the presidential election, it also complicates talks among business executives over tax policies and government spending.

Ryan has been revered by U.S. business leaders for his message of smaller government and reduced regulatory burdens. The National Federation of Independent Business, which represents small businesses, gave Ryan a score of 71 out of a possible 100 on congressional votes it monitored last year. The U.S. Chamber of Commerce also gave Ryan good marks the same year.

MORE: Is Obama or Romney a better leader? How to judge.

But when it comes to how to reduce the U.S. deficit, corporate America has generally pointed to the 2010 Simpson-Bowles plan, which is strikingly different from Ryan’s vision in many ways. This isn’t much of a surprise, since Ryan, who served on the commission that proposed Simpson-Bowles, led a block of three House Republicans who rejected it.

But while the plan came up short of votes needed to go before Congress, it has nevertheless gained considerable attention, if not respect, in the business world. CEO heavyweights from Jeff Immelt of GE (GE) to Jamie Dimon of JPMorgan (JPM) to Dave Cote of Honeywell (HON) (who was a member of the Simpson-Bowles commission) have supported the plan that would blend spending cuts with tax increases to wring $4 trillion from federal deficits over the coming decade. Admittedly, many have said the plan isn’t perfect, but it at last serves as a blueprint for tackling the deficit. Even Romney himself has endorsed the plan his running mate rejected, saying as recently as Aug. 2 that “my [deficit reduction] plan is very similar to the Simpson-Bowles plan.”

Indeed, there are some similarities between Ryan’s plan and Simpson-Bowles, but perhaps more on principle than specifics. Both generally aim to simplify the tax code and control government spending. But for CEOs that have been backing Simpson-Bowles, its uncertain if they’ll be able to overlook a few key differences between the two plans. And whether corporate America will start referring to Ryan’s plan as a model over Simpson-Bowles.

MORE: Paul Ryan’s private equity backers

For one, the plans differ on tax code reform, says Marc Goldwein, senior policy director for the Committee for a Responsible Federal Budget, a part of the New America Foundation, an independent, nonpartisan policy institute that has supported the Simpson-Bowles plan.

Ryan’s plan would use all savings from spending cuts to finance other cuts. By contrast, Simpson-Bowles would actually take some savings from reducing the deficit to generate about $1 trillion more in revenue over 10 years than today’s tax code would allow.

They also differ in the area of defense spending, Goldwein adds. Whereas Simpson-Bowles looks to cut deeply into military spending and generally safeguard programs for the poor, Ryan earlier this year pushed a bill through the House that would fend off year-end cuts to military spending by squeezing from food stamps and other social safety-net programs. As The Wall Street Journal notes, Romney has not embraced the bill.

Ryan wants to turn food stamps into block grants, giving states a set amount of funds to cover the Supplemental Assistance Program. Further, starting in 2016, recipients would be required to work or enroll in a job-training program and a limit would be phased in.

Given the differences, it remains to be seen how Corporate America will respond to Ryan-ism. Admittedly, not all CEOs buy into all the details of the Simpson-Bowles plan, including Honeywell’s CEO, who thought the plan didn’t go far enough to curb spending. And it didn’t address costs of Medicaid, he said in an interview with Fortune in September 2011. Ryan has said he wants to turn Medicaid into a block grant, similar with his vision for food stamps.

However CEOs take it, Ryan’s jump onto the campaign trail certainly puts the deficit at the forefront – with all its complexities.