Taxi drivers at National Airport, angered by alleged harassment by U.S. airport police, yesterday threatened a work slow-down or strike if their demands are not met by July 31.

A two-hour meeting between representative of the drivers and Federal Aviation Administration officials yesterday left both sides disappointed.

"We're very mad. We wasted two hours of our time," said driver Theresa Marroum. "They kept saying they'd look into it, but they needed specific incidents. We have the majority of the cabdrivers behind us, and we'll get all the documentation they want."

J.J. Brown, president of the Northern Virginia Cab Drivers Association, said, "We're prepared to take very strong action on July 31 - possibly a strike or slow-down."

The dispute between the drivers and the FAA police - who have feuded repeatedly over traffic and parking problems in the congested airport circle - centers on the alleged misconduct of officer Robert Conrad, who the drivers are seeking to have dismissed from the force.

Conrad has been accused of pulling his gun on cabdrivers, beating a woman driver on the head with a taxi radio microphone and using abusive language and racial slurs against the drivers, many of whom are black and foreign-born.

"When we have specific written complaints on Officer Conrad, we will conduct an investigation," said airport manager Hugh Riddle after the meeting. He said he was unaware of misconduct on the part of any of the FAA police. "But the charges are serious enough to take a look at. I don't like to see this kind of unrest. A strike would mean a great deal of inconvenience to the traveling public."

Although Riddle called yesterday's meeting "productive," he said the investigation into Conrad - who has reported receiving threats on his life - and other alleged incidents of harrassment would not begin until the complaints were more specific.

"They're just too general now," he said, adding that he had not heard of any such complaints before yesterday's session with the drivers.

Along with the dismissal of Conrad, the drivers are demanding an end to alleged police harassment, permission to step out of their cabs while lining up to pick up fares, and the installations to bathroom facilities for the drivers.

"They think because they drive people in and out that they are airport employes," said Riddle. "They're not. They're independent contractors. I admit the situation is undesirable, but it happens every summer. It's hot. Tempers are flaring. It's a pressure-packed atmosphere. We're hoping for harmonious relations."

Asked how the current feud would be settled, Riddle shook his head. "I really don't know," he said.