Robert McArthur was about to collect his cab fare from the two passangers early yesterday when he felt the cold steel of a gun barrel against his head.

With some reluctance, McArthur gave the mand with the gun $40, a day's work. But instead of fleeing, the man pointed the gun at the cabbie's face and pulled the trigger.

A loud crack broke the early morning silence -- and Robert McArthur lived to tell the tell about it with only the left lens of his eyeglasses shattered and his nerves a bit rattled.

The gun, as it turned out, was a starter's pistol, and the bullet was only a blank.

"I knew that if I knew anything at all, I must have been all right," said McArthur, recollecting his thoughts after the shooting. "I figured that I must have been all right because if I wasn't then I was dead."

The incident occurred at 2:30 a.m., bar-closing time in Washington, McArthur said. The young man and woman who flagged him down at the corner of Franklin Park at 14th and I streets NW seemed harmless enough. Yet, by his own admission, McArthur, 45, should have known better.

A veteran of five years as an independent cabbie, he was robbed and stabbed in 1978, but managed to sit on his assailant until the police arrived. His reputation as a savvy cabbie soared and he made several television appearances to tell his story.

According to McArthur, yesterday's encounter began as a pleasant ride into far Northeast, filled with light banter about the woman's pending trip to Hawaii and her companion's loving admonition not to be left alone here. Both were security guards working late, McArthur said they told him.

He said the woman eventaully called the cab to a halt in a parking lot in the 3700 blodk of Jay Street NE.

When McArthur turned to collect the fare, he felt the gun barrel against the back of his head. Then the woman left the cab, he said. Alone with the gunman, McArthur told him that he was not going to give up the night's earnings until he was sure the man had a gun.

"My father was robbed by a man with a Coke bottle, and he never stopped talking about that," McArthur recalled yesterday. When the cabbie saw the gun, he gave up the money.

D.C. police said yesterday they had no suspects in the robbery, one of a growing number of holdups in the city. Robberies are up to 40 percent in Washington this year, and armed robbery is one of the most common fears of city hackers.