Jack Gannon used to go to the hardware store carrying a notebook and sharp pencil so he could scribble notes to salesclerks asking the size, location and price of items he needed. Now Gannon shops from his home and in a few minutes orders nails, lumber, paint and plumbing supplies from the Hechinger Co.

Gannon's shopping has become easier because an increasing number of stores have installed TDD machines, telecommunications devices for the deaf, to assist deaf customers like himself. Government agencies have also installed the machines.

From their homes or offices, the deaf can now order groceries, clothes, airline and railroad tickets and even car mufflers from dozens of local businesses that have TDD machines.

TDD is the general term for machines that resemble typewriters and are connected to a telephone receiver. The older models are called teletypewriters (TTYs). The caller and the receiver type their messages, which are transmitted through the telephone line.

Deaf persons who own a TTY or TDD can directly communicate with department stores, insurance agencies, doctors, dentists, lawyers and others in Maryland who have installed the machines.

There are an estimated 10,000 to 15,000 TDDs in use in the Washington area, according to a survey of companies that sell the equipment. About 103,000 people in this area have significant hearing losses, 42,000 of them living in Montgomery and Prince George's counties.

Gannon, a Silver Spring resident and director of alumni relations at Gallaudet College -- the world's only accredited liberal arts college for deaf students -- said the growing number of TDDs here has helped him considerably.

"Now I don't have to drive over to the store every time I have a question on a sale or need to know if something is in stock," he said.

While business use of TDDs is fairly recent, the emergency police and fire number, along with schools, county governments and major utilities, have had TDDs for the past decade or longer. Federal law requires that most public agencies have TDDs available, and Metro and Amtrak are required to have TDDs for taking reservations. The Metro rapid rail system is also considering installing TDDs at pay telephones at three subway stations.

The 911 police and fire special emergency number in Montgomery and Prince George's counties is connected to a TDD that receives a few calls a week in each county, officials said.

Many Maryland hospitals -- including Montgomery General, Prince George's County General, Doctors Hospital of Prince George's County, Washington Adventist, Leland Memorial, Greater Laurel-Beltsville, Shady Grove Adventist and Northern Arundel hospitals -- have TDDs, usually in the emergency room or admissions office.

Stores as diverse as Sears Roebuck, J.C. Penney, Midas Muffler, Giant Food and Goodyear Tire have TDD machines, which cost from $300 to $500 each.

"Businesses want to tap the deaf market," said Muriel Strassler, who is deaf and director of public information for the National Association of the Deaf, based in Silver Spring.

The number of TDDs in area businesses is growing "at a fairly good pace as people become more familiar with them," she added.

The major local directory of TDD numbers lists about 250 businesses with the machines. Of those, about half are in the Maryland suburbs, with 30 in the District and the remainder in the Virginia suburbs.

Potomac Electric Power Co., Chesapeake and Potomac Telephone Co. and the Washington Gas Light Co., the area's largest public utilities, have provided TDD service to the deaf since the mid-1970s.

Pepco estimates that it receives 14,000 calls a year, while C&P reported receiving an estimated 10,800 calls a year and Washington Gas about 230.

Pepco and C&P receive large numbers of calls because they offer a third-party calling service for the deaf. Deaf people can call one of the utility companies and ask them to call a business, a doctor or an office that is not equipped with a TDD. The utilities make the calls and then relay the information back to the deaf person.

"Less than 1 percent of the calls we get on the TDD are related to Pepco business," said employe Dolores Caniglia. "We make appointments and check on jobs."

The Sears catalogue ordering service gets 25 calls a week. Giant Food's TDD line averages seven calls weekly, including orders for deli party platters, cakes and drug prescriptions at one of the chain's 132 stores. The Washington Post has three TDD lines to place classified ads, to check on subscriptions and to get answers to other questions.

Hechinger's store at the Hechinger Mall in the District installed a TDD in late December and now averages six calls a day. The number of calls will be monitored to determine if the machines should be placed in other Hechinger branches, said store manager Hudie Fleming.

But the Hecht Co. department store chain found that its TDD line was seldom used and discontinued its TDD number last year.

"Some group health insurance companies now have TDDs, so it is easier to reach my doctors," said Marla Hatrak, who is deaf the and manager of special services for the U.S. Senate. She recently spent three days trying to find a lawyer because of delays in getting through via an interpreter.

As TDD usage increases, merchants with TDDs concede that they are still learning how the machines work.

"It's really enlightening to see all these calls come in," said Fleming of Hechinger's. "A lot of people are just phoning to tell us they're glad we've put a TDD in."