At 6 feet 5 inches tall, Joe Muldoon stands out in a crowd. He's not bashful about it; he enjoys the attention, so being pictured as 12 feet tall is almost twice as much fun.

Muldoon, the owner of the Potomac Polo Club in Poolesville, is one of the more conspicious subjects of a 100-by-15-foot mural being painted in Rockville on the side of a $35 million redevelopment project.

The mural, entitled "Sunday Afternoon," depicts more than 50 persons riding or saddling horses, playing in the sun or watching a polo match at the club where Muldoon said about 2,000 spectators watch polo action every Sunday between May and October.

Designed by commercial artist Terry Rodgers of Gaithersburg, the mural is scheduled to be completed in about two months. To anyone driving by on Rte. 355 or using the Metro station across the street, the unfinished version looks like a gigantic jigsaw puzzle with a couple of pieces missing.

Painting began three weeks ago on the building, which is called the Rockville Metro Center and will include office space, restaurants, shops and movie theaters when it is completed in 1986.

The mural was the idea of Warren Eisinger, general partner of Eisinger-Kilbane & Associates, the developing company that owns the building. The mural will cost the company $120,000.

Rodgers has been working on the project for a year. It started with hundreds of photographs taken at the polo club where polo matches are held every Sunday from May to October on Muldoon's 700-acre farm in Poolesville. Muldoon saw the mural for the first time yesterday.

"There I am, larger than life," he said. "It's amazing. It really captures the exact flavor of what happens every Sunday both on the field and off. It's a close resemblance . . . . It's kind of nice to stick out in a crowd. It's an honor. I would have been jealous if I wasn't in it."

On the far left side of the mural, Muldoon leans against a truck with his arms folded as a group of horses that look like they are about to run onto Rockville Pike kick up dust as they carry their riders in the middle of the mural.

To the right, a yet unpainted crowd including Rockville Mayor Viola D. Hovsepian, who says she has never seen a polo game, will be shown enjoying the match from the grandstand. Eisinger's friends and relatives are scattered among the crowd.

Rodgers has hired three artists from a private New York company to do the actual painting. He will refine parts of their work later, but spends most of his time six days a week directing the artists and taking frequent glimpses at a 38-inch poster of the painting he keeps tucked under his arm.

"I called Terry because I knew he was interested in doing commercial art, and I said, 'I got this big wall out here. Think about it,' " Eisinger said.

Rodgers, 37, came back with an idea for an abstract painting that neither he nor Eisinger was eager to talk about yesterday. Eisinger felt abstract art would not be appropriate.

He wanted something more realistic, and Rodgers suggested a mural of a polo match because he always wanted to capture horses, athletes and the kind of people who attend the event.

Eisinger, who has been playing polo since he was 13 years old, loved the idea, especially because Rodgers depicts him scoring a goal in the mural. Rodgers said he welcomed the chance to do his first exterior mural. Large murals, he said, are rarely found on the East Coast.

"I like the opportunity to do work on this scale," Rodgers said. "It doesn't have to sit in someone's office or living room. This is a public piece of art. It's open to everybody."

Yesterday, at least one passerby said he liked what he saw.

"It adds a lot of character to Rockville, especially this area," said Steve Tyler of Gaithersburg. "It beats looking at all those high-rises."