The Bush administration has been unable to muster even half the 2,500 National Guardsmen it planned to have on the Mexican border by the end of June, officials in the border states said.
The head of the National Guard Bureau disputed that tally and said the goal would be met by Friday.
As of Thursday, the next-to-last day of the month, fewer than 1,000 troops were in place, according to military officials in Texas, California, New Mexico and Arizona.
President Bush's plan called for all 50 states to send troops. But only 10 states — including the four border states — have signed commitments.
Some state officials have argued that they cannot free up Guardsmen because of flooding in the East, wildfires in the West or the prospect of hurricanes in the South.
"It's not a combat priority. It is a volunteer mission," said Kristine Munn, spokeswoman for the National Guard Bureau, an arm of the Pentagon, "so it's a question of balancing the needs of the Border Patrol with the needs of 54 states and territories, and all those balls roll in different directions."
Bush's plan called for 2,500 troops to be on the border in support roles by June 30, and 6,000 by the end of July. But officials in the border states said the Guard won't reach the 2,500 target until early to mid-July and will likely need longer to meet the 6,000 mark.
"The magical numbers coming out of Washington are not going to happen, definitely not by Friday," said Maj. Paul Ellis, a spokesman for the Arizona National Guard.
A White House spokesman declined to comment, referring questions to the National Guard Bureau.
Later Thursday, Lt. Gen. H Steven Blum, chief of the National Guard Bureau in Washington, issued a statement saying that the Guard "will have 2,500 Army and Air National Guard members supporting Operation Jump Start in the four border states," by Friday.
"Reports to the contrary are factually incorrect and ill-informed," his statement said.
Blum's spokesman, Daniel Donohue, said he could not account for the state reports about the lagging numbers. He suggested Guardsmen serving in support roles, such as cooks and others, may have been overlooked.
Lower troop numbers and gaps in deployments could mean fewer Border Patrol officers will be able to focus on catching illegal immigrants as planned. Bush had said the mission would free up thousands of officers now on other duties to actively patrol the border. Guardsmen are expected to build fences, conduct routine surveillance and take care of other administrative duties for the border patrol.
Munn said nearly 1,800 troops were committed to the mission. But Guard officials from California to Texas said more than half have yet to reach the border. At least 600 are weeks away from getting there.
Only six non-border states — Arkansas, Delaware, Kentucky, Montana, Tennessee and Wisconsin — have officially joined the mission.
In recent days West Virginia, New Jersey, North Carolina and Arkansas pledged troops, but many of those would not arrive until sometime next month, said Tom Koch, a New Mexico National Guard spokesman. On Thursday, Virginia announced that about 350 National Guard members had volunteered.
Major problems began to appear last week when California, which has already committed to sending 1,000 troops, said it turned down an administration request for 1,500 more to cover expected shortfalls in the numbers sent by Arizona and New Mexico.
Gov. Arnold Schwarzenegger's spokesman, Adam Mendelsohn, said the state is leading all others in contributing troops and the shortfalls are not California's responsibility.
"The governor is prepared to do whatever it takes to secure California's border," he said, "However, at the start of fire season, we cannot send troops to New Mexico and Arizona and other states when we already have 1,000 troops committed to this."