Defending champion Paul Erhardt of Fraser, Pa., fashioned a three-under-par 67 in between fog and rain that plagued the Middle Atlantic Amateur Golf Championship at Washington Gold and Country Club yesterday. It gave him a four-stroke lead in the 72-hole, medal-play tournament.

About half the field of 107 starters was caught in a heavy afternoon downpour that forced suspension of play for nonfinishers until this morning. The greens were under water on the final hole and there was water covering parts of other fairways.

Erhardt, a 38-year-old owner of an auto equipment parts company, finished before the rain started. He was four strokes ahead of local favorites Marty West and Henri deLozier, both of Columbia County Club, and Bob Kotz of New Jersey and Jim Millar of the host club.

The Middle Atlantic, one of the oldest amateur tourmanents in the country, having first been played in 1902, produced some high scores on the tight Washington course that measures a deceptive 6,104 yards.

"Frankly," said Erhardt, "this course is not my kind of track, but then I should not be complaining. It seems I play my best golf in the fall. I play a lot of tournament golf in this Washington area and it's been lucky for me because I've won this (Middle Atlantic) tournament before and I consider this one of the best fields in the country."

Erhardt missed only two greens and had 32 putts. He ran off eight straight pars and then birdied the ninth, a par-3, with a six-iron and a four-foot putt. He birdied the 10th from 10 feet and the 11th from six feet. He caught his only bogey on the 13th when he went over the green and missed a five-foot comeback putt. He birdied the 17th when he put a four-iron shot 12 feet from the hole and made it.

West had two birdied and a bogey going out in 34. He came back in 37 when he nullified another two birdies with four bogeys. DeLozier had two bogeys and a birdie on the front, and one birdie and a bogey on the front, and one birdie and a bogey on the back. "The greens are slow and hard to read," he commented.