The looming suspension of an estimated 250,000 New York driver’s licenses with fraudulent Social Security numbers pitted national security concerns against immigrant rights in a charged Assembly hearing yesterday.

Since January, as part of a national effort to collect and verify driver’s licenses, the New York Department of Motor Vehicles has sent out 495,000 letters at the rate of 4,000 a day to individuals whose Social Security numbers did not match a national database.

DMV Commissioner Raymond Martinez, drawing on the September 11 commission’s recommendation that standards be set for the issuance for sources of identification, defended the sweep as crucial to protect against future terrorist attacks.

“Licensed documents, issued in states where requirements were less stringent than those here in New York State, allowed the hijackers to board airplanes and execute their acts of terrorism against our nation,” Mr. Ramirez said. “As a result, we at DMV, along with most other state DMVs throughout the nation, have re-examined our licensing and identification requirements and procedures to make sure we are doing everything we can to protect our citizens.”

The action has uncovered one Buffalo man responsible for more than $100,000 in bank fraud who had obtained 15 different New York driver’s licenses and nondriver ID cards, hundreds of New York city taxi drivers with multiple licenses, and a Queens resident who collected more than $100,000 in fraudulent insurance claims and sold fake ID packages starting at $800.

The sweep has also uncovered internal fraud. “It is a constant battle against employee malfeasance,” Mr. Martinez said.

Advocates testified the much greater impact has been immeasurable hardship to hundreds of thousands of immigrants, a detrimental effect on national security by pushing immigrants further underground, and the loss of thousands of low-income jobs.

Further, by using Social Security cards as a measure of immigration status, advocates charged the DMV with overstepping its mandate.

“We strongly support efforts to increase our national security, but we believe restricting access to licenses is an inefficient way to enforce immigration laws and prevent terrorism,” said the executive director of the New York Immigration Coalition, Margie McHugh.

Immigrants, who had traveled from around the state, packed the hearing and protested outside the building at City Hall Park.

“It doesn’t only affect me, but every member of my family,” said one Peruvian immigrant who works as a taxi driver as he tearfully recounted receiving a letter informing him he could no longer drive. “What is happening to immigrants is a slow death.”