He will be the only invited governor on either side of the border to skip the event. Last year, Bush hosted the gathering when it took place in Texas.
Bush has cultivated warm trade and cultural relations with Mexico that for years have been the envy of other border states, particularly California. The front-running Republican presidential candidate has made his state's strong ties to Mexico part of his overtures to Hispanic voters.
But when the border governors convene Sept. 9 in Tijuana, Mexico, Bush will be the keynote speaker at an anniversary celebration for a church in the Dallas area, said Bush spokeswoman Mindy Tucker.
"He would have gone, but he had already agreed to attend the event for his friend Tony Evans," Tucker said.
The Rev. Tony Evans is co-founder and pastor of Oak Cliff Bible Fellowship Church in Dallas and a prominent speaker in Promise Keepers, a national evangelical men's group. He and Bush are friends who sometimes pray together in person and on the phone.
The Sept. 9 celebration, marking both Evans' 50th birthday and the 30th anniversary of his ministry, is taking place so late that Bush won't be able to attend day two of the border conference either, Tucker said.
The 17th annual border conference will focus on cross-border infrastructure, bolstering the image of the border region, protecting the environment and preparing for natural disasters.
"I think it will be a good time for them to come so we can expand all the relationships between the states, and fortify them," said Patricia Sahragui, a spokeswoman for Alejandro Gonzalez Alcocer, governor of the Mexican state of Baja California.
But she said she understood Bush's decision. "This event has been scheduled for a lot of months, but we can understand things that can be in their way, so they can't attend."
In July, Bush decided not to appear at a national conference of minority journalists in Seattle, even though he was already in town. Stung by criticism from conference attendees and from the news media, he reversed himself and showed up.
A few weeks later, he angered some in the Hispanic community when he declined to speak to the National Council of La Raza, a Latino advocacy group. Bush was vacationing in Maine at the time.
But Bush has made several trips to Mexico to meet with its presidents, and on Friday, he plans to appear with President Ernesto Zedillo at the opening of a new bridge on the Texas-Mexico border. On Thursday he will attend a Latin Business Association luncheon in Los Angeles.
With Bush absent, the other three U.S. governors will take on higher profiles. Gray Davis of California, Gary Johnson of New Mexico and Jane Hull of Arizona said Tuesday that they will attend, joining six Mexican governors.
The gathering will have speial significance for Davis, who has made a point of improving California-Mexico ties after the tenure of California Gov. Pete Wilson, whom many Mexicans distrusted for his attempts to halt illegal immigration.
When Davis replaced Wilson this year, one of the first things he did was travel to Mexico City and Monterrey, Mexico, to bolster trade, education and cultural links.