Washington (CNN) -- President Barack Obama asked Congress on Tuesday to approve $600 million in emergency spending for steps to increase security along the border with Mexico, a key issue in the immigration reform debate.
In a letter to House Speaker Nancy Pelosi, Obama said the money would pay for hiring 1,000 new border patrol agents and 160 new Immigration and Customs Enforcement agents, two unmanned aircraft systems and other support for border security.
Obama's letter also said the spending would be partially offset by canceling a $100-million Homeland Security program that the president described as "lower priority."
Republican critics complain that Obama has failed to devote proper resources to border security, which they say contributes to an untenable flow of illegal immigrants into the country from Mexico.
Obama contends that border security is one aspect of comprehensive immigration reform needed to deal with the illegal immigration issue.
Last month, administration officials disclosed that Obama planned to deploy up to 1,200 more National Guard troops to the border with Mexico and request the additional money referred to in Tuesday's letter.
A previous troop deployment to the border region, called Operation Jump Start, ended in 2008. The operation sent more than 6,000 troops to California, Arizona, New Mexico and Texas to repair secondary border fence, construct nearly 1,000 metal barriers and fly Border Patrol agents by helicopter to intercept illegal immigrants.