It was 4 p.m. and Winfield M. Kelly Jr., promoter and politicians, was talking about salesmanship as he sipped his second glass of Dubonnet.

"To me, it's the thrill of the big sale, the thrill of bringing the big piece of bacon home," the Prince George's County executive said as he gazed across W. 53d Street from the bar in the New York Hilton.

Kelly's product is Prince George's County. He sees a buyer behind every tree. "We're getting a new Cadillac dealership in the county," he extolled. "To most people that sounds like just another auto dealership. But we've never had a Cadillac dealer in Prince George's. That shows things are changing. That shows progress."

Kelly had spent the day trying to peddle Prince George's County on the streets and in the corporate offices of New York.

The effort was hardly awe inspiring. One of the two meetings he had scheduled with New York firms had been canceled at the last minute. The other began with a rift over whether a reporter should be allowed to sit in on the session.

Even more damaging. Kelly and company had learned at noon that a Japanese industrialist, interested in building a factory, had popped into the county about the same time they had arrived in New York. Frantically, Kelly's press aide and alter ego, John Lally, had telephoned back home with the message that the entourage was willing to return home if a meeting could be arranged with the president of Kawasaki Co. It couldn't. In effect, Kelly had missed the big fish in the backyard pond by going trolling on the high seas.

But Kelly is an optimist, an unabashed hometown booster. The mere idea that a group of businessmen and county officials should have the audacity to go to New York boosted his spirits. And by the time he caucused with the Prince George's County Economic Development Committee at 6 p.m., he declared unabashedly, "I guess it's been a damn successful day."

"It's safe to say a trip like this will have a multiplier effect," chimed in Sonny Long, the committee chairman.

There were a couple of hopeful notes. One J.C. Penney vice president told Kelly his company is planning to build a major new shopping center in the county, and Arlen Co., the owners of Prince George's Plaza in Hyattsville, showed the group plans for a multimillion-dollar effort to convert the aging shopping center into an enclosed mall.

But these had little to do with any economic development effort by the county - work on Prince George's Plaza began last week, in fact. "You don't have to sell us on Prince George's County or the Washington area," said Lawrence C. Bibb, vice president of JCP Realty, a Penney subsidiary. "We already have two stores there and we'd like more."

Actually, the economic development game is a game of mirrors. No one knows exactly what works and what doesn't. Kelly and company have dug about as far as anyone into the gimmickery bag to come up with ways to peddle the county.

With a budget of $274,000, they've concoted a new name for Prince George's County - "Baltington," a place they describe as perfect for princely corporations, halfway between Washington and Baltimore in the nation's fourth largest market; hired an economic development staff, launched an advertising campaign in Business Week. Forbes and Fortune: and are now visiting such corporate centers as New York.

It's all part of Kelly's "New Quality" campaign, a piece of hometown boosterism designed to change the county's image as Washington's blue-collar suburb and perennial underdog.

Kelly is tailor-made for his role. He is a young hustler, who grew up in family of 14 children in the Washington suburb of Mount Rainier and became a millionaire in the mobile hot-lunch business - his lunch wagons were called "Winnie's Chuck Wagons."

Now that he's made it in the business and political worlds, he wants his home county to become "a solid, middle-class county with pride."

The object of the New York trip, he said on the plane up there, was to "stimulate interest in the county" and "set a tone that we are a county with a willingness to work with business."

But if Prince George's wants to roll out a red carpet for New York, New York this week didn't exactly roll out the red carpet for the county.

When Kelly, Long, Kenneth Neil, a builder, and Joseph O'Mara, an architect, arrived at a meeting with J.C. Penney executives, they were greeted at the elevator not by an executive or even a receptionist, but by locked doors, a 1984-looking television screen and a disembodied voice that said, "Welcome to J.C. Penney," and directed them to stand in a white spot in the middle of the floor. After a few awkward moments, face came on the screen and asked who they were and what they were doing.

"I felt like part of the gang that couldn't shoot straight," Kelly joked later.

The next problem was that Bibb, the Penney executive whom the group was meeting, turned white when he learned a reporter was with the group.He said he had been incorrectly quoted once by another newsman with a similar group from another city and wasn't about to take any chances.

He then ushered the newsman out of a sterile-looking conference room to his sterile-looking office overlooking Central Park. A poster on the wall there said, "I know that you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant." It was signed by Bibb.

Forty-five minutes later, Bibb emerged from the meeting with Kelly and company.He was pleased by their visit, he said. "My interpretation of what they are doing is they want us to come to town, and they want us to know they're interested in us," he added later. "I wish some other jurisdictions in the Washington area would show the same interest. We've felt quite frustrated in dealing with some parts of the Washington area."