Discount taxi shuttle service to and from the Rosslyn, Crystal City and Pentagon City Metro stops during rush hour is being initiated this week in Arlington.

The Diamond Cab Co. has begun offering the shuttle service at less than half the cost of regular metered service to many Arlington destinations. The Red Top Cab Co. will offer similar door to door service starting Feb. 6.

Cabs will pick up commuters at their homes and will be either continually cruising past the three stations or waiting there for riders during the rush hour periods from 6:30 to 9:30 a.m. and 3:30 to 6:30 p.m., according to Ken Hook, supervisor of Arlington public works planning. If no cab is waiting, commuters may call one, under the new program.

Once a cab picks up a passenger at any of the Metro stations, it will be permitted to wait 10 minutes for another passenger going to the same vicinity. If none appears, the original passenger gets private service for the discount price, according to Hook. The cab companies say they need three passenger per trip to break even.

Commuters wishing to catch a cab to the stations must phone the cab company at least an hour before they wish to be picked up.

Under the new program, which Diamond began offering Monday, the county is divided into seven zones, and fares are to be calculated according to the zones in which the trip originated and ended.

A trip that does not cross a zone boundary will cost 90 cents, while a trip across one zone line will cost $1.25. A trip that crosses two zones will cost $1.95. Normal Virginia cab rates are metered and depend on the distance of the ride.

Harold Oakes, who is supervising the program for Diamond, said the new zone program could save the commuter half the usual taxi fare, which is $1.20 for the first mile and 10 cents for each seventh of a mile after. A meter trip from the Rosslyn station to the Fairfax-Arlington boundary could cost up to $5. Under the zone plan the commuter would pay $1.95 for the same trip, he said.

Wholey said the Arlington County Board approved the new taxi fare system on Oct. 15 because it is more efficient than using individual cars.

Hook said that all cab companies in the county were notified of plans for the program but only Red Top and Diamond responded. CAPTION: Map, METRO TAXI SHUTTLE - Map shows zones into which Arlington is divided under new taxi shuttle program. A person catching a cab at the Rosslyn Metro station may travel anywhere in Zone 1 for 90 cents, anywhere in Zone 4 for $1.25 and anywhere in Zone 5 and 6 for $1.95. A commuter at the Crystal City or Pentagon City stations can go anywhere in one 2 for 90 cents, anywhere in Zone 3 for $1.25 and any where in Zone 7 for $1.95. Rates to the stations would be the same.