The Ford maverick roared down Massachusetts Avenue in Washington at 1:30 a.m. yesterday and Geraldine Robertson turned to her boyfriend, Anthony Blackwell. They were not going to make it to the hospital in time to have their baby, she said.

"But he kept saying just be quiet and still, we'll make it," she recalled.

He was wrong. Near the main post office, they were stopped for speeding and running a traffic light by U.S. Capitol police officer James L. Queen. "She's going to have a baby," Blackwell screamed to the officer, who in turn radioed for help.

Capitol police officer Douglas Pippin was cruising in his scout car a few blocks away."I got a woman delivering a baby," he heard Queen say on the radio. Pippin rushed to the scene at North Capitol Street and Massachusetts Avenue.

"I went over to see if I could help out," said Pippin, who had delivered a baby before. "The lady was definitely ready. I asked her how close the pains were coming, but she couldn't tell me. I timed them with my watch. They wre less than a minute apart."

Pippin told the woman to lie down on the front seeat with her head in the direction of the steering wheel. He grabbed a banket from his car and placed over her.

Officers Queen and J. R. Smith held flashlights overhead to help him see. A crowd of postal workers gathered.

"I was pushing," Robertson said yesterday from her room at George Washington University Hospital. "They told me to breath hard. I was scared to death."

"We had to shift her around a bit," Pippin said. "It was definitely hurting her. It was strictly natural (childbirth)."

A few minutes later, Pippin said he could see the top of the baby's head. "I turned the baby's head to make sure the cord wasn't choking her," he said. "She came out crying."

When the baby cried, the postal workers, who had gathered clapped and cheered. "You got more guts than I have," a postal worker told Pippin.

When it was announced that the baby was a girl, the women in the crowd cheered. "It was wild," said Blackwell, who held Robertson's hand and comforted her during the ordeal. "I almost fainted."

Pippin cleared the baby's mouth with his finger and gauze. "I was about ready to cut the umbilical cord when the ambulance arrived," Pippin said. They took over from there.

As Robertson was being placed on the stretcher and carried to the ambulance, she said she noticed the crowd. "Someone said you should be a proud mother," she said. "All I could do was throw up my hand and wave."

Hospital officials said yesterday the baby is healthy and fine. The baby, who weight 7 pounds and 10 ounces, has been named Porsche. She was dressed in a white gown and had a bow in her hair as she slept in a bed in the hospital's nursery.

"It was a big experience," said the 19-year-old Robertson, who lives at 53 Hanover Pl. NW. "We would have been in trouble if the police had not pulled us over."

But, Blackwell still maintained that he probably could have made it to the hospital if the police had not stopped him. "If I had two more minutes, we would have made it."

For Pippin, the whole experience was close to home. His wife is expecting their first child in September. "It was fun," he said. "It was actually a lot of fun."

Pippin said he delivered a baby about 12 years ago when he worked for a funeral home that handled ambulance service in Abingdon, Va. He said he had been reading literature on childbirth broiught home from the doctor by his wife.

"She wants me to be in the delivery room when the baby is born," he said. "I think I can do that after this morning's incident."