The former park officials say current regulations requiring that visitors to national parks render their weapons inaccessible were working well and have helped make national parks among the safest places in America.
"These rules, promulgated during the Reagan administration, are essential to park rangers in carrying out their duties of protecting park resources and wildlife, and in assuring the safety of visitors to the parks," the letter said. "In all our years, we experienced very few instances in which this limited regulation created confusion or resistance."
The letter is signed by park service directors dating back to the Johnson administration, including the past four park chiefs. Among those signing the letter is Fran Mainella, who led the park service from 2001 to 2006.
Interior Secretary Dirk Kempthorne said in February that his department will review gun laws on lands administered by the National Park Service and the Fish and Wildlife Service. Officials will draw up new rules by April 30 for public comment, Kempthorne said.
The National Rifle Association and other gun-rights advocates have pushed to relax the gun rules, which ban loaded firearms in national parks. The regulations, last changed in the early 1980s, require guns to be unloaded and placed somewhere that is not easily accessible, such as in a car trunk.
The review of the gun rules follows letters from half the Senate complaining about the gun restrictions. The senators - 41 Republicans and nine Democrats - say the current rules are confusing, burdensome and unnecessary.
Last November, in a letter to the House Committee on Natural Resources, current National Park Service Director Mary Bomar expressed support for the regulations, stating they "provide necessary and consistent enforcement parameters throughout the National Park System."
The National Park Service said there were 116,588 reported offenses in national parks in 2006, the most recent year for which data are available, including 11 killings, 35 rapes or attempted rapes, 61 robberies, 16 kidnappings and 261 aggravated assaults.
There were more than 272 million visitors to the nation's 391 parks, monuments and recreation sites in 2006, the agency said.