Chain link fences erected last week dividing Alexandria from Fairfax County on two streets in the Baileys Crossroads area were denounced yesterday as "arbitrary, discriminatory and invalid" and likened to "Checkpoint Charlie" as the Fairfax County Board of Supervisors decided to sue to get rid or them.

The Alexandra government raised the 5-foot-tall barricades to stop what it perceives as an increasing number of Fairfax County commuters cutting through the Downden Terrace neighborhood to get to Shirley Highway. The county claims commuter traffic has not increased significantly and views the fences as an extreme traffic control measure.

"They're absurd, those barricades," said Fairfax Supervisor Alan I. Magazine (D-Mason), in whose district lies half of Downden Terrace. "It looks like Checkpoint Charlie out there."

The county's suit asserts that the barricades "endanger the health, safety and welfare" of Dowden Terrace residents who are covered by Fairfax fire and rescue services under a reciprocal agreement between the two jurisdictions.

Fairfax Fire Chief George Alexander said he would testify in court that Fairfax firemen's response time into Dowden Terrace could be cut by a minute in some cases because of the fences.

The suit also alleges that the city failed to follow proper public hearing procedures before erecting the barricades and did not follow its own criteria for closing streets.

Alexandria Transportation Director Dayton Cook said the city's criteria for street closing includes a provision that the City Council can "change the criteria as it sees fit."

"They (the county) should have expended this much energy years ago to put up the bypass they promised and didn't deliver," Alexandria Mayor Frank E. Mann said. "They promised over and over that the road was a reality and we found out it was an out-right lie."

Mann was referring to a letter to the city in late May from Virginia Department of Highways and Transportation Commissioner John E. Harwood that sid no money would be available to build a bypass around congested Baileys Crossroads.

The City Council voted to erect the barricades shortly after receiving the letter, and they went up June 12.

Some Dowden Terrace residents say their lawns have been marred by speeding cars and some pets have been hit.

"If we closed every street where a cat had been hit we'd all have to stay at home," said Magazine, who called the barricades "arbitrary," discriminatory invalid."

Alexandria's transportation office records show the number ofcars moving through the city's side of Dowden Terrace had increased by about 3,000 cars to 12,500 a week in the past year.

State statistics show the annual traffic increase in Dowden Terrace to be not greater than 8 percent, an increase considered normal for Northern Virginia, Magazine has said.

In other action yesterday, the board scolded Chairman John F. Herrity for a delay in signing a letter from the supervisors to the school board, asking for reconsideration of a 6 percent pay increase given to schoolemployes.

Although the letter was dated June 2, the school board did not receive it until last Friday, 10 days after a June 6 deadline when teacher contracts including the 6 percent pay increase were mailed out. The school board notified the supervisors that it is now impossible to reconsider their action.

Herrity said he had been unaware of the June 6 deadline and added that the criticism of him "looks to me like political games aimed to embarrass me." Herrity won the Republican 8th District congressi onal nomination in a primary election last Tuesday.