For $31, a pair of prescription eyeglasses can be purchased at For Eyes, a discount optical office at 1829 M St. NW.Two blocks away at Malamut Opticians, 1990 K St. NW, the price for eyeglasses with the same prescription and similar frames was $72.50.

Between those extremes is a range of prices for essentially the same eyeglasses, a survey of seven Washington stores in the same neighborhood showed -- $32 at Peoples Drug Stores, 717 14th St. NW; $56 at Sterling Optical, 1215 Connecticut Ave. NW; $62 at Pattyson & Wright, 1908 K St. NW; $65 at Franklin & Co., 1700 K St. NW; and $68 at Classic Optical Center, 1895 L St. NW.

The savings -- and the wide range of prices -- are possible today because of a combination of circumstances both locally and nationally that are favorable to consumers.

For one, states now permit prices to be advertised. And the right to advertise prices has led to a rapid growth in discount optical shops and marketing that promotes competition and price cuts.

Consumers, consequently, can in many cases sharply reduce the price they pay for their eyeglasses by shopping around -- often in the same neighborhood or in the downtown Washington area.

Tom Andreasen, general manager of Malamut Opticians, said yesterday that his price -- the highest of the seven shops surveyed -- reflected quality and service.

"A $10 frame can look like a $100 frame -- but it won't wear like one," he said. The same is true of lenses, he said.

About 115 million people -- roughly half the U.S. population -- wear corrective lenses. In the metropolitan Washington area, about 1.5 million wear glasses or contact lenses.

Today when consumers shop for eyeglasses, they find:

Drugstores fill prescriptions for eyeglasses as readily as prescriptions for medicine. In the Washington area, both Peoples Drug Stores and Dart Drug Corp. have opened optical centers at many of their stores.

Coupon specials aimed at attracting customers. Dart Drug, for example, includes in its advertisements a coupon worth $25 toward the purchase of a pair of eyeglasses.

Specials good for a limited time. Sterling Optical in downtown Washington displays on its counter a group of discontinued frames which are on sale for $40 -- a price that includes the prescription lenses -- so long as the supply lasts.

The competitiveness that has hit the eyewear market has taken hold since the Federal Trade Commission in the mid-1970s took aim at state laws banning advertising of prices. It has brought more than cosmetic changes to the industry, however.

Sales have increased, and the average prices that consumers now pay for eyewear make it one of the few bargains left in today's inflated economy.

"There's no doubt that the price has been substantially lowered," said Frank Rozak, vice president of the National Association of Optometrists and Opticians, a trade group of chain optical firms.

Statistics from the U.S. Consumer Price Index show that during 1979, when the rate of inflation across the United States rose to 13.9 percent, eyeglass prices went up only 6.6 percent.

Some new problems for consumers have turned up, however.

Deceptive advertising, misleading prices and the possibility of poor quality at some outlets are among the hazards that consumers must pick their way through when they search for bargain eyewear, according to Federal Trade Commission Officials.

Nancy Baker's experience is one example of the headaches that can be caused by vast price differences in look-alike products.

The Montgomery County mother of two bought eyeglasses recently at an optical chain recommended by a friend. She paid $185 -- $55 for large plastic frames and $130 for oversized bifocal plastic lenses.

Baker was satisfied with her purchase until she bumped into a friend at a school meeting. "The woman next to [the friend] was wearing eyeglasses that cost $27 -- and they didn't look much different from mine," Baker said.

In fact, they were different, Mrs. Baker found. The other eyeglasses consisted of single-vision lenses and frames, while Mrs. Baker's lenses contained graduated bifocals spread throughout the lenses rather than being concentrated in one portion of the lenses.

The impact of advertising on the price of contact lenses has been even more dramatic, said Terry Latanich, an FTC attorney. "They used to be $400; now they can be purchased for less than half that," he said.

Although most officials in government and industry agree that the market now offers lower average prices, the quality of eyewear still is shrouded in questions.

One FTC report issued last year found that there was no significant number of errors in low-power eyeglasses dispensed by any of the optical offices surveyed. About 5 percent of the low-power eyeglasses checked failed a test for error.

The medium-power eyeglasses had a higher percentage of errors. About 20 percent of them failed, but the FTC said that isn't a significant number, either.