WASHINGTON — Flights were delayed by up to two hours across the country on Monday, the first weekday that the nation’s air traffic control system operated with 10 percent fewer controllers. Pilots, gate agents and others were quick to blame furloughs caused by mandatory across-the-board budget cuts, but the Federal Aviation Administration said it was too soon to tell.

The agency said in a statement, however, that “travelers can expect to see a wide range of delays that will change throughout the day depending on staffing and weather-related issues,” and that there were special “staffing challenges” at radar centers in New York, Dallas-Fort Worth, Jacksonville and Los Angeles. At those centers, controllers had to space airplanes farther apart so that they would not have to take on more planes than they could manage at a time.

The F.A.A. said it would not have a firm count of how many delays were the result of air traffic control staffing until Tuesday.

The agency said the public can get a snapshot of overall delays at its Web site, faa.gov.

Delays piled up throughout Monday as the airlines, including US Airways, JetBlue and Delta, were forced to cancel some flights because of cutbacks. Shuttle flights between Washington and New York were running 60 to 90 minutes late. But Southwest Airlines said it did not see any unusual delays.