A 23-year-old messenger who made pickup and deliveries on her bicycle was killed yesterday when her 10-speed bike collided in Georgetown with a 10-wheel truck full of gravel.

The victim, Mary Gaffney of Bethesda, worked for the Call-A-Messenger service of Silver Spring, and was a familiar figure in the downtown Washington area to both customers and those who saw her on her rounds.

The collision occurred about 10:15 a.m. at 29th and M streets NW, while Gaffney was pedaling east on M Street and the westbound truck was making a left turn from M Street onto 29th Street, D.C. police said.

The driver of the truck, identified as Walter A. Patterson, 50, of 714 Chaplin St. SE, was given a traffic ticket charging failure to yield right of way, police said.

Gaffney, whose father, James J. Gaffney, is a retired supervisor in the Washington field office of the FBI, was a 1975 graduate of Walter Johnson High School in Bethesda. She received a bachelor's degree in December from the University of Maryland.

Gaffney, who lived at the family home on Singleton Drive, had just completed a bicycle trip in the Great Smoky Mountains and was riding about 50 miles a day to prepare for a bicycle tour of Europe.