Head professional Jack I. Walker operates the pro shop in a construction trailer, but he already is swamped with requests for golf lessons at the Herndon Centennial Municipal course, which opened a week ago.

Of the four municipal courses in Fairfax County, only Herndon has a PGA Class A professional running the operation.

"I'm amazed at the number of persons who want to take lessons from a PGA pro," said Walker, former head man at Duke of Marlborough, where he also began humbly, in a trailer.

The clubhouse at the new Eddie Ault-built Herndon course should be completed Nov. 1. Now, Walker has a snack bar with vending machines, and a pro shop housed in a 60-foot trailer.

"I'd like to get into a teach program because a lot of juniors out here want lessons," said Walker, whose younger brother Chuck is head pro at Falls Road in Mopntgomery County.

"I'd like to get the people who don't play and the junior players just starting. They are very easy to teach; someone who has never had a club in their hands. You can kind of build their swing."

At the grand opening, 60 golfers appeared and staged a drawing to determine the inaugural foursome. All four of 'em hit it down the middle, that was kind of unusual," Walker said.

The par-71 course measures 6,445 yards from the blue tees, on 135 acres, and cost more than $3 million to construct. A driving range is open by day, with lights likely to be constru cted.

Directions: Take Rte. 7 from Tysons Corner six miles toward Leesburg, left on Rte. 606 toward Herndon and proceed three miles, turn right on Ferndale Avenue, which takes you to the course.

The new course should relieve a crowded situation at Algonkian and draw some players from Reston South, Goose Creek and Twin Lakes, among others. The layout is about two miles from Dulles.

Greens fees are $2.75 for nine, $5 for 18 on weekdays; $3.35 for nine, $6 for 18 on weekends. For seniors on weekdays, the charge is $2 for 9, $4 for 18.

Defending Maryland Open champ Gary Marlowe will have his hands full with 141 amateurs and pros in the 54-hole stroke play tournament beginning tomorrow at Hillendale in the Towson area.

The last professional to win the event, Chris Pigott, is preparing to buy a home. The Prince Georges assistant has been too busy working and teaching to hone is game.

The Open's amateur entrants are headed by Marlowe, at 19 the youngest ever to win the event, Marty West (who recently won his fourth Maryland Amateur) and Larry Rentz.

Marlowe's father Tony, head pro at Woodmont, is among pros entered.

Other pros include George Graefe, who won as an amateur in 1976; Mark Alwin, Middle Atlantic PGA titlist; U.S. Open participants Ken Leber and Randy O'Linger; Brad Shiefelbein, Larr Ringer Dennis Satyshur, and tour player Peter Chapin.

"We try to set the course up in a championship manner," said Maryland State Golf Association President Dick Latimer. "They let the rough grow and sometimes the greens are double cut. We try to make it a difficult but fair test."

Latimer said six pins would be placed in a difficult spot, six less severe and six relatively easy. The tees are moved back every day.

Who said the PGA tour lacks flair, with players named Monte Carlo Money, Rocket Rockett and, would you believe, Buzz Fly?...The fifth annual Irish Open July 18 at Glenn Dale will benefit the Steve Dean Scholarship Fund at Georgetown University ... East Potomac head pro Bill Linton offers free lessons for boys and girls ageds 10-16 in July ... The top four finishers in the Bobby Bowers Junior starting tomorrow at Springfield qualify for the World Series of Junior Golf ...

Kathy Padgett of Laurel Prines took the scenic route in shooting 80 at Columbia, to win the Middle Atlantic Golf Association girls' championship for the second straight year. Padget, who played on the golf team at Laurel High, had four birdies and an eagle. She drove the green on the par-4 17th hole and holed a six-foot putt for deuce.