WASHINGTON » Senators working on a bipartisan immigration bill have agreed to require fingerprinting when foreigners leave the country through any of the nation’s 30 busiest airports.

It’s a step toward the more expansive biometric system favored by many senators but deemed too expensive to include in the bill.

Under the amendment by Republican Sen. Orrin Hatch of Utah, the nation’s 10 busiest airports would have to establish a fingerprinting system within two years. Within six years it would have to be in place at the 30 busiest airports.

The amendment passed 13 to 5 today as the Senate Judiciary Committee plunged into its third week of deliberations on the immigration legislation.

Lawmakers have cited the absence of a reliable system to track people coming and going as a major security flaw.