Franks, former commander of forces in Iraq and Afghanistan, faulted Kerry's votes on major weapons systems and intelligence issues, and against the 1991 Gulf War.
"If his voting record ruled the day, Saddam Hussein (search) would not only be running Iraq but Kuwait," Franks told about 200 people Sunday at a Reno rally.
"The choice is very, very clear. We need decisive, strong, no-backing-down and no-equivocating leadership," he said.
Franks praised the Democratic challenger's military service during the Vietnam War, but said Kerry's later anti-war activities upset him.
"The men I served with in Vietnam weren't war criminals and I'm proud I served with them," Franks said.
Kerry spokesman Sean Smith accused Franks of distorting Kerry's Senate voting record.
"He reads (Bush political aide) Karl Rove's talking points very well," Smith said. "John Kerry voted for the largest defense appropriation in American history and the largest intelligence appropriation in American history. No matter how many attacks they make on John Kerry, it won't obscure the fact that George Bush has gotten us into a quagmire in Iraq."
Kerry never branded any U.S. troops in Vietnam as war criminals, Smith added.
"The men who served with him in Vietnam are with him in his campaign and have been with him for 35 years," he said. "I think that says it all."
The rally in Nevada — a battleground state where polls show Bush and Kerry running about even — marked Franks' first appearance for Bush since the Republican National Convention.
Franks, a registered independent in Florida who has voted for both Republican and Democratic presidential candidates, said he decided to endorse Bush because of his handling of the war against terrorism.
Other terrorist attacks during the Clinton administration went largely unanswered by the U.S., he said.
"I know a commander in chief when I see one and there's only one on the ballot," Franks said. "After September 11th, we were blessed to have a commander in chief who said enough is enough.
"There are two options: to fight them (terrorists) over there or to fight them over here. I'm an over-there-kind-of-guy," he said.
In an interview before the rally, Franks said he doesn't foresee an endless cycle of violence in Iraq, and he thinks violence will diminish after the Nov. 2 election.
"I believe they (insurgents) are influenced by what they see in our media," he told The Associated Press. "They see if they blow something up it's front-page news ... (and) the presidential candidates will talk about it.
"After Nov. 2, that dynamic will leave. The problem won't go away, but it'll be diminished ... This will be a long process, but there will come a time when the insurgents have less opportunity to create mischief for us," he said.
Franks said he also expects the January elections in Iraq to be held as scheduled, and foresees the day when U.S. troops will leave there.
"Some say that day will never come, but I say it'll come and probably sooner than later," he said. "(But) we ought to stay away from time frames and time schedules. The quickest way to give an advantage to the enemy is to set deadlines."