Advocates for tougher immigration enforcement plan to confront the commander of the Arizona National Guard about why troops backed off recently as gunmen approached their post near the Mexican border.

Maj. Gen. David Rataczak is to testify Monday before the state Legislature's homeland security committee in a hearing about the Jan. 3 encounter at an observation post.

While National Guard officials and supporters say the troops did as they were supposed to, critics question the point of having the troops on the border if they can't confront such dangers.

The encounter has broader border security implications because armed people will know the National Guard will retreat, said state Rep. Warde Nichols, the committee's chairman.

"From every account I can get, it appears they were testing our resolve and what our men at the border would do," said Nichols, a Republican.

Rep. Steve Gallardo, a Democrat on the committee, said he believed immigration hard-liners would use Rataczak's appearance to push their agenda.

"They are going to try and embarrass him. They are going to fail," Gallardo said.

Four National Guard soldiers from Tennessee were at a lookout post at the border when they were approached by six to eight gunmen wearing bulletproof vests. One of the gunmen came within 35 feet of the observation site, according to investigators' summaries.

The soldiers contacted Border Patrol agents and pulled back, investigators concluded. The Border Patrol tracked the armed men back to the border but could not locate them. No shots were fired.

Democratic Gov. Janet Napolitano, National Guard officials and some state lawmakers defended the decision to call in the Border Patrol, saying the troops are not supposed to perform law enforcement duties. The governor's office has said the rules allow Guard members to use force when they believe they face an imminent threat and all other means are exhausted.

"I don't think that it's up to the committee to negotiate the rules of engagement," Napolitano said. "Those rules of engagement were negotiated with the National Guard at the federal level."

The troops were among the 6,400 National Guard members sent to the four southern border states to support immigration agents, and leave the agents with more time to catch illegal immigrants.

The support duties include monitoring border points, assisting with cargo inspection and operating surveillance cameras.

"We don't apprehend," said Maj. Paul Aguirre, a spokesman for the Arizona National Guard. "We don't detain. We don't transport."

Aguirre objected to characterizations of the withdrawal as a retreat, saying the soldiers did not run from their post and were not overrun.

The troops monitored the situation, never lost contact with the gunmen and moved to another site to avoid an engagement, Aguirre said.