Twenty-four workers at Triborough Bridge tollbooths became ill over the last four days, and the city is monitoring the air near the booths. No motorists are reported to have been affected.

A spokeswoman for the Environmental Protection Department, which is testing the air, said normal readings were obtained for carbon monoxide, carbon dioxide and other pollutants and hazardous materials. ''So far it's still a mystery,'' the representative, Tina Casey, said.

The booths are to be in normal operation today, a spokeswoman for the Triborough Bridge and Tunnel Authority, Barbara Richardson, said.

The attendants, 23 of whom were treated at hospitals, had complained of scratchy throats, nausea, headaches and dizziness. A vice president of the Bridge and Tunnel Officers Association, Peter Lukas, said the air in the booths would be tested today for sulfur compounds.