How cold is it?

It is so cold that an emergency order of 100 little electric blankets is being flown in from the West Coast to thaw out Metro's balky, multimillion dollar farecard-vending machines.

Because when it is cold, the farecard-vending machines refuse to accept dollar bills.

"I can see what will happen when you reporter guys get hold of this," one top Metro official said yesterday. "You'll probably write a story that says "Brrrr." in the first paragraph, or something smart like that."

Farecard vending machines are those 4-foot-by-8-foot monsters that stand just outside the gates to the Metro train platforms. They are arrayed with red and green lights, white buttons, glass and printed white instructions. It all looks very promising until the time comes for the machine to take a dollar bill.

Then, in cold weather, the machine simply refuses. "It's a severe problem," Nicholas Roll, Metro's assistant general manager for transit services, said yesterday.

The coin slot accepts coins without difficulty.

The problem, according to Metro and Cubic Corporation officials, is that the piece of equipment that accepts bills, called a validator, doesn't like cold weather. Cubic Corporation, a San Diego firm, has the $53.2 million contract to provide Metro with fare collecting equipment.

"Each machine has an environmental control system," said Cubic's man in Washington, Gary Roberts. "It is supposed to operate down to 23 degrees. The validator operates only down to 40 degrees, but there is a little heater in the machine that makes up the difference."

"The temperature," he said, "has dropped below the average to whcih we had engineered and manufactured our equipment." (The low reading Wednesday at National Airport was 16.)

The most hard-hit machines are located in outdoor stations such as Rhode Island Avenue and National Airport. However, some underground stations - notably at the pentagon, the Federal Triangle, Judiciary Square and Dupont Circle - also have balky machines.

Thirty-nine of Metro's 224 farecard vending machines refused to vend yesterday.

Light bulbs have been installed in some machines to warm up the validators. The small electric blankets, Roberts said, will be wrapped around the validators after they get here from San Diego today.

The cost, Roll said, is Cubic Corporation's.