WASHINGTON — The controversial roundup of illegal aliens working at Salt Lake City International Airport before the 2002 Olympics was not an isolated incident but the first of many nationwide in a search that identified more than 5,000 illegal aliens who lied to obtain jobs in sensitive areas from airport tarmacs to military bases and nuclear power plants.

Federal officials, according to a new report, managed to arrest only about a fifth of that number.

The report, issued Thursday by the U.S. General Accounting Office, a research arm of Congress, looked at problems with tracking people who enter the country legally but overstay their visas. It says the Department of Homeland Security figures the number of "overstays" in America is now 2.3 million, which the GAO says is probably underestimated significantly.

"Tracking system weaknesses make it difficult to monitor potentially suspicious aliens who enter the country legally," the GAO said, or even realistically estimate their numbers, which creates potentially huge security problems.

As an example of risks, the GAO report pointed to the number of illegal workers identified at airports nationally. "Of the 4,918 unauthorized workers identified (in roundups), 1,054 have been arrested, and 3,864 others have left their airport jobs and eluded arrest," the report said.

The GAO said that after the 9/11 attacks, federal authorities discovered in some early work that many people working for passenger-screening companies were illegal aliens.

"As a result, further sweeps began in 2001 with Washington, D.C., and Salt Lake City in preparation for the 2002 Olympics," the report said. "These eventually became known as Operation Tarmac and are still ongoing."

The Dec. 12, 2001, bust of 271 workers at Salt Lake City International resulted in 69 arrests; 202 workers were fired. The sweep sparked protests from the leaders in the local Latino community, who said foreign workers were unjustly targeted and their families hurt by the operation that left some families without parents or income.

"As of April 2004, DHS (the Department of Homeland Security) reported that 195 airports had been investigated and 5,877 businesses had been audited," identifying the 4,918 workers who were illegal aliens.

The GAO said additional research it did on 26 selected airports showed that about a third of those actually arrested had first entered the country legally but overstayed visas or other permission to enter the country.

For example, it said 23 of the 48 people arrested at Salt Lake International Airport were "overstays."