Mark Alwin, an assistant pro at Congressional, one-putted seven times on the back nine and shot 67 for the first-round lead of the 54-hole Maryland Open golf tournament yesterday at Bethesda Country Club.

Alwin, 32, twice a winner of the Middle Atlantic Open and the Middle Atlantic PGA but never a winner at Bethesda, said he putted well all day but could not get any birdie putts to drop on the front nine. Alwin shot one-over-par 36 on that side.

Alwin said he thought he was in for more putting frustrations on the back nine when he left his birdie putt on the 10th hole hanging on the lip of the cup. But he sank a 12-foot birdie putt on the par-5 No. 11, a three-footer for birdie after a sand wedge approach on the 12th and a 15-footer for bird following an eight-iron to the green on the 15th.

He ran in a "cross-country" 55-foot putt for birdie on the 17th, and completed the back nine in four-under-par 31. Alwin used just 11 putts on those nine holes, compared with 17 on the front.

Bill Winters, a 30-year-old assistant at Robin Dale who was out of golf for three years with an injured right elbow, shot 68, good for second.

Veteran Paul Masca of Font Hill overcame hooking problems, which sent him two over par after five holes. He made four birdies and totaled 69. Amateur Gary Marlowe of Woodmont tried to backhand in a three-inch putt at the seventh hole, missed, and took double bogey, tying at 70 with two-time champion Larry Ringer of the Naval Academy. Defending champion George Graefe of Crofton shot 73.

The field of 139 was cut to 71 for today's second round.