WASHINGTON - The Bush administration has sharply ratcheted up prosecutions of illegal immigrants along the U.S.-Mexico border in the past year, with increases so dramatic that immigration offenses now account for as much as half of the nation's federal criminal caseload.

In the widening crackdown, administration officials prosecuted 9,350 illegal immigrants on federal criminal charges in March, a 73 percent increase over prosecutions last year and an all-time high, according to statistics released Tuesday. Convicted people have received jail sentences averaging about one month. MORE