Immigration agents arrested four suspected leaders of an illegal alien smuggling ring in their latest crackdown, which pushed the number of detainees past 500.

Immigration and Naturalization Service spokesman Ron Rogers said the four suspects arrested with 21 illegal aliens at a south-central Los Angeles "drop house" - where aliens are kept until they can be moved around the country - Tuesday night were "key principals" in the alien smuggling network."We believe one of the larger smuggling rings was broken up in the operation," he said.

Further details were to be released by INS Western Regional Commissioner Harold Ezell at a news conference.

INS agents combed the five key Southern California airports Tuesday night, arresting 26 aliens at Los Angeles International Airport and 14 others at Ontario International Airport, some 35 miles east of downtown Los Angeles, Rogers said.

Agents also were assigned to the Burbank-Glendale-Pasadena Airport, Long Beach Airport and John Wayne-Orange County International Airport, but no arrests were made.

More than 430 immigrants have now been arrested in the Los Angeles area since the crackdown began Feb. 27, INS officials said. Nearly 100 others were taken into custody in sweeps elsewhere in the country, including Atlanta, Charlotte, Las Vegas, Boston and Phoenix.