The National Guard troops assigned to the Arizona border will begin to arrive Aug. 1, and the federal government is sending other reinforcements to stem the flow of illegal immigrants and narcotics entering the state, Homeland Security Secretary Janet Napolitano said.

Napolitano is announcing today that hundreds of additional Border Patrol agents and customs officers are being deployed to prowl the Arizona outback and operate inspection stations. She said Immigration and Customs Enforcement will open a new office in Ajo. And the Department of Homeland Security is sending a new team to Douglas.

"We are also reassigning major technology assets, including mobile surveillance systems, thermal-imaging binocular units, and trucks equipped with detection scopes, as well as observation and utility aircraft," Napolitano says in a guest column in today's Arizona Republic.

A government official, who declined to be named because he was not authorized to divulge details, said the secretary is assigning more than 300 Border Patrol agents and port inspectors to the Tucson Sector. In addition, 100 ICE personnel will be added statewide. The official said the staffing increases will result from personnel shifts and do not represent new positions.

He said six aircraft and dozens of mobile surveillance, thermal-imaging and other smuggling-detection devices also are being reassigned to the Tucson Sector.

This spring, the Obama administration announced its plan to deploy the National Guard soldiers. During a meeting with Brewer in June, administration officials said up to 1,200 troops would be assigned, with 524 of those operating in Arizona. They will be used primarily in port-screening operations and as criminal analysts.

The beefed-up enforcement is expected to begin just as Arizona implements a controversial new immigration law that is under assault in federal court on constitutionality grounds.

Napolitano's announcement also comes amid statewide political campaigns dominated by immigration-related issues, with Democrat and Republican leaders complaining about Arizona's status as a smuggling corridor.

Gov. Jan Brewer, Republican Sens. John McCain and Jon Kyl, and Democratic Rep. Gabrielle Giffords have been among the outspoken elected officials clamoring for heightened enforcement. Because Napolitano's announcement was provided to The Republic under an agreement to not publish a story until today, reaction from members of Congress, border sheriffs, immigrant-rights groups and others could not be immediately obtained.

Amid a national furor over illegal immigration and drug-cartel violence, the Obama administration has sought to demonstrate its commitment to border security by beefing up enforcement. At the same time, the president and Attorney General Eric Holder have advocated immigration reform and challenged the legality of Arizona's new law.

The law, scheduled to take effect July 29, makes it a state crime to be in the country illegally. It states that an officer engaged in a lawful stop, detention or arrest shall, when practicable, ask about a person's legal status when reasonable suspicion exists that the person is in the U.S. illegally.

Napolitano repeated previous assertions that the U.S.-Mexico border has become more secure, not less, in the past few years. "Despite what those looking to score political points may tell you, the numbers show we are moving in the right direction," she wrote. "Last year, illegal crossings along the Southwest border were down 23 percent. . . . And, by all measurable standards, crime levels in U.S. border towns have remained flat for most of the last decade."

However, Napolitano conceded that the Tucson Sector, which covers most of Arizona's southern flank, is a funnel point for human and drug smuggling because of heightened enforcement elsewhere along the border.

The administration is still seeking congressional approval for an additional $600 million to enhance Southwest border security: 1,000 new Border Patrol agents (500 in Arizona), 160 additional ICE agents (50 in Arizona), two unmanned aerial- detection systems and a dozen temporary teams of agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The House has approved funding; Senate consideration is pending.

Arizona's border with Mexico spans about 360 miles, with security fencing along 306 of those miles. About 17,000 Border Patrol agents are assigned in the Southwest, double the number of seven years ago. Arizona has nearly 10 agents for each mile of boundary with Sonora.