Alexandria police have increased patrols in shopping areas by 60 percent this month to combat the traditional rise in street robberies over the holiday season.

City police created a special Robbery Task Force several years ago to combat the seasonal crime increase. The task force draws officers from all over the Public Safety Department's police arm and assigns them to patrol duty. In addition to providing high police visibility in robbery-prone areas, the program gives officers a chance to work outside their regular assignments for six to eight weeks.

Since the task force was instituted, robbery statistics show a decrease. In November 1982 there were 51 robberies of all types in Alexandria. In November 1983 that figure fell to 35. There were 52 robberies in December 1982, a number that fell to 39 in 1983.

Capt. Larry Brohard, who heads the task force, says it has two objectives: maintenance of a high police profile and prevention of robberies wherever possible. A 1982 police study shows that certain areas become robbery-prone during the holiday season. Brohard concentrates his troops on those locations: the West End shopping centers such as Landmark, Van Dorn Plaza and Bradlee; the Mount Vernon Avenue Corridor; and the Old Town commercial area, centered around Washington and King streets.

From mid-November to the beginning of January, the Robbery Task Force increases by nearly 60 percent the number of officers on patrol in Alexandria. Most of the officers are assigned foot patrol duties in the robbery-prone areas. The rest are assigned vehicles, and cover larger areas overlapping those patrolled by the foot officers.

The task force is divided into two groups: a core group, assigned to the task force full time, and a larger, rotating goup of officers who work with the program on a part-time basis. Officers in the core group are temporarily transferred from their reqular assignments for the duration of the program. The officers come from all police branches, including officers from personnel and training.

According to Brohard, two factors contribute to the seasonal increase in crime: the holiday shopping season and the change from Daylight Savings Time to Standard time. For this reason, high-visibility patrols are assigned to the Braddock Road and King Street Metro stations, as well as the shopping areas. "People are walking two or three blocks in the darkness from mass transit," Brohard says. These people, used to walking either to their cars or homes in daylight, are more vulnerable to robbers.

In addition to the task force, Alexandria also works to improve the efficiency of the officers regularly on duty with the Directed Patrol concept, in which officers are not only assigned beats, but told to concentrate on specific areas within those beats when not responding to a call. For example, patrols at both Metro stations are beefed up between the hours of 4 and 8 p.m., when particular attention is paid to pedestrian traffic.

Brohard says most street robberies occur in the early evening hours. Women are particularly vulnerable, and most of the robberies are purse snatchings. He advises women to be careful to hold their purses securely.

A would-be robber needs both the "opportunity and desire to steal," Brohard says. The Robbery Task Force and Directed Patrol programs strive to take away opportunity with high-visibility patrols.