The two Predator drones will be used to patrol the border and in nearby areas in the Gulf of Mexico, once Congress approves the 500 million dollars President Barack Obama has requested, Napolitano said in a Washington speech.
"These types of flights aren't necessary everywhere," she said in comments to the Center for Strategic and International Studies. "But this is the case in the Texas border."
The United States currently has four drones patrolling the border with Mexico in Arizona and one in the northern border with Canada in the state of North Dakota, according to the Department of Homeland Security.
Napolitano said the new aircraft are part of a reinforcement of border patrol efforts including one thousand additional agents and 60 investigators.
"Over the past 18 months, this administration has devoted more resources -- including manpower, technology and infrastructure -- to the Southwest border than at any point in America's history," she said.
Texas Governor Rick Perry had requested delivery of the planes, which the US used extensively in Afghanistan and Pakistan.
The Obama administration is seeking to step up security as it presses for a comprehensive immigration reform measure that likely would allow many of the millions of illegal migrants in the United States to legalize their status.
Many Republican lawmakers say no immigration measure can be considered unless the federal government can ensure security along the southern US border to prevent a spillover of violence from Mexico.
Napolitano also announced a number of new cooperation agreements with law enforcement in non-border states to send personnel to southwest border.
DHS said it is working on a system that will fully link the information systems of all state, local and tribal law enforcement entities operating along the southwest border with those of the federal government.
"Border security is primarily a responsibility of federal government," she said. "We cannot have 50 different state legislations. It will not work."
The remark was aimed at a controversial Arizona law that allows police to question persons suspected of being illegal immigrants.
The agency said it was developing "Project Roadrunner," a license plate reader recognition system aimed at detecting drug trafficking and associated illegal activity along the border.
In a related comment in Congress, Democratic Senator Robert Menendez said the security situation will influence the debate on immigration.
"There are those in the Senate who believe we should basically
militarize our borders and until we do, until we meet some standard of
militarization, we cannot tackle the issue of comprehensive
immigration reform," he said.