PHOENIX — Gov. Janet Napolitano is balking at putting Arizona National Guard units along the international border at state expense to replace troops from across the nation who are being withdrawn.

Napolitano said Tuesday that U.S. Homeland Security Secretary Michael Chertoff has ignored her request to delay the planned en this summer of Operation Jump Start.

That federally funded program, started in 2006, was designed to put 6,000 Guard soldiers in support roles along the border — 2,400 in Arizona — to do projects ranging from surveillance and office tasks to building fences. The idea was to free up Border Patrol officers to actually get out in the field.

All those troops, however, are slated to be gone by July 15.

 The governor said while that deadline may have made sense when the program started. But she said it does not make sense now.

 “I think given the delays in getting the ‘virtual fence’ operational, given the delays in getting the Border Patrol staffed up to the numbers that were predicted, removing the Guard is premature and unnecessary,’’ she said.

 The governor said the number of people being apprehended trying to cross the border illegally has been decreasing. “And we think one of the reasons is because they know the Guard is there to back up the Border Patrol.

Napolitano acknowledged there is an alternative: She is the commander of the Arizona National Guard. And that gives her the power to order the soldiers under her command onto active duty to replace those Guard units which are being withdrawn.

But the governor said one big difference is who picks up the bill.

“Since I believe the federal government has not put enough federal resources on the border to begin with, to put yet anothe burden on Arizona taxpayers would be a hard thing to swallow,’’ Napolitano said.

Still, she said the idea of perhaps having Arizona Guard units do some of their required annual training along the border “is not outside the realm of possibility, but nothing I want to commit to right now.’’

“We’re still working on the feds,’’ she said.

 But what Napolitano wants just isn’t going to happen, said Laura Keehner, a spokeswoman for the Department of Homeland Security. “This has been our plan all along,’’ Keehner said Tuesday evening, to increase the Border Patrol while decreasing the number of Guard soldiers along the border.

 She also rejected Napolitano’s contention that the build-up of federal officers has been slower than anticipated. Keehner sai the Border Patrol is on track to have 18,000 officers working by the end of this year, the precise number projected when Operation Jump Start started.

 Keehner also said that virtual fence near Nogales — a network of sensors, radar and remotely operated cameras to track people and vehicle crossing the border — is working.

 “We’ve apprehended over 3,000 people just in the 28 miles in this testing area since December,’’ she said.

 “There was a small, six-month delay,’’ Keehner continued. “But it has been working ever since,’’ saying some media reports of problems have “misrepresented’’ the scope of the problems.

 “The cameras and the radars and the sensors are all individually working just fine,’’ she said. “It was a temporary problem of making sure they all worked together and that has since been fixed a long time ago.’’

 And Keehner said while the system initially was identifying cattle and wildlife as illegal border crossers “that was a temporary problem that was fixed long ago.’’