The contest for market share and consumer loyalty among major drug chains in metropolitan Washington soon may be fought on a new battleground in what is already regarded as the most competitive market in the country.

Consider the following developments that have come to light in recent days:

* Washington-based Peoples Drug Stores Inc., the area's leading drug chain, has added a new service for blind customers by putting Braille labels on prescription drug containers.

* Giant Food Inc., the area's leading supermarket chain, will open what could be the first of several free-standing pharmacies next week in Bethesda. Giant already operates 41 pharmacy-food combination stores in metropolitan Washington

* Sherwin-Williams Co., which acquired floundering Drug Fair last year, served notice yesterday that its drug chain division will mount an aggressive expansion and merchandising campaign here.

Without exception, chain operators emphasize innovation and service as the keys in their bids to grab bigger shares of the market.

Giant and Peoples are recognized widely for their aggressive merchandising and innovative programs. But Drug Fair had been a question mark in the year or so since it merged with Gray Drug of Cleveland, which was subsequently acquired by Sherwin-Williams.

Indeed, the transition and development of expertise in the industry and this market hasn't been easy, a Sherwin-Williams spokesman acknowledged recently.

The giant paint products company actually acquired two unprofitable companies when it bought Gray and Drug Fair, the official noted.

"My impression is they're sleeping," Kenneth M. Gassman Jr. of Wheat First Securities recently said of Drug Fair's new management.

"They're slipping badly," another industry watcher observed.

An official at Sherwin-Williams acknowledged that "sales were soft when we first acquired Drug Fair" but added that "there hasn't been any dropoff in sales in the past few months."

With Sherwin-Williams behind it, the new Drug Fair will be a formidable competitor, the official indicated.

"We have an aggressive commitment to the Washington market," she said.

Although Gray Drug maintains some corporate functions here, it fired several former Drug Fair officials and consolidated activities in Cleveland. Industry observers concluded that that decision cost the Gray-Drug Fair combination substantial market share and profits.

After installing new management to run Gray Drug, Sherwin-Williams has named a new vice president in charge of the drug-chain division's Atlantic region. The new structure will ensure increased emphasis on "regional needs and opportunities," a spokesman said.

Proof of Sherwin-Williams' commitment to the Washington market soon will be apparent, the official said, in an aggressive acquisition of existing properties and space in new projects.

In addition, Drug Fair plans a substantial increase in its promotional budget and activities here.

"In terms of how we are responding to the competition in that market, we are looking closely at service being a differentiating quality for us," the Sherwin-Williams official said. "Everybody talks about service, but we plan to make it a reality. We plan that it will not be a cliche."

Ultimately, the contest for customer loyalty could be a boon for consumers. Peoples, already a leader in health care services, is a step ahead of the competition with the introduction of the Braille labels. "We try to be innovative," said Peoples' President Sheldon Fantle.

Meanwhile, Peoples is in the process of installing computers in its stores, which will enable pharmacists to build customer profiles from prescriptions. "The [computer] terminal gives us the capability to provide a far more professional service to our prescription customer," said Leonard Demino, vice president for professional services at Peoples.

The new computers also will provide better inventory control, facilitate third-party billing and improve record-keeping.

Giant's new pharmacy, like all of the chain's other stores, will be equipped with a computer that performs similar functions.

Although Giant officials have not indicated their plans for the future, the new pharmacy, in which specialty foods and flowers also will be sold, may be operated as a test unit for future stand-alone drug stores.

Regardless of what happens, "We plan to hold our own," a Sherwin-Williams official vowed. "We are going to give [the other chains]a run for their money."