Old Town Alexandria merchants have grown accustomed, they say, to occasional break-ins and bank robberies.

Even in the prim, historic section around N. Washington Street, where homes and stores, have been rehabilitated in the traditional red brick colonial style, businessmen have accepted what appeared to be a growing crime rate.

But the murder Thursday of Carol Ann Dodd, the victim of an apparent robbery of her optical store less than a block from Robert E. Lee's boyhood home, left nearby store owners shocked.

"I could't believe it," said Marijke Telekamp, a friend of Dodd's who, since 1964, has operated Telekamp opticians a block away near bustling King Street. "Things like that don't happen around here. Banks get held up. But an optician?"

Dodd was not the kind of person to have made any enemies or to have resisted a robbery, acquaintances say. At the time of her murder, she probably had little more than $100 cash in the store. "That's the thing that's so silly," said Ron Benjamin, an optician with Telekamp who had worked for Dodd for five years. "Probably 80-90 percent of our business is in checks and charge plates. Optical places don't have any money, Particularly Carol.

"She'd be at the store at 8:30 in the morning to ring out the cash register, then go to the bank to make a deposit," he said.

Yet at 2 o'clock Thursday afternoon, while scores of automobiles passed by on the city's main thoroughfare and resxidents stood waiting at several nearby bus stops, someone walked into Brahm Opticians, apparently forced Dodd to empty her cash register and open her safe, then shot her in the back.

Police said yesterday they have no witnesses and no suspects in the slaying.

"To me, its very frightening," said Dianne C. Yeatman, manager of the Washington-Lee Saving & Loan two doors from Dodd's shop. "People say, 'Don't you want to leave Old Town?' And I say no, because I really like it down here.

"But lately," Yeatman said, "things have really gotten out of hand. They've really broken wide open."

The apparently growing crime rate seems to some merchants particularly disturbing. In most cases, care has been tken to retain the area's charm.

The banks surrounding Brahm Opticians are furnished with colonial-style furniture and brass chandeliers.

Security measures are more in keeping with the leisurely pace of country living than with the rest of urban Washington.

"This is one of the better parts of town," said James E. Merritt, manager of a savings and loan across the street from the scene of Thursday's shooting. o"That's why it's so unbelievable that something like that would happen.

"We've had robberies," Merritt said. But never anything that violent. It's not a violent neighborhood."

Only three weeks ago, Dodd's store was burglarized and she installed a security system to prevent a recurrence. "We were all kind of unnerved because of the break-in," said Whitney Mirsch, who managed Dodd's second store on Seminary Road.

In the last year, robberies in Alexandria have increased dramatically, compared to other crimes. Along with rapes, their frequency is running counter to trends for other crimes in the city.

In the first six months of 1980, for instance, the number of major crimes reported to police -- including homicides, assaults and burglaries -- was down about 10 percent compared to the same period a year ago.

The drop in July was 16.5 percent. This year, however, robberies are up 25 percent and rapes more than 50 pecent. In June, robberies increased 56 percent over the same month the year before.