A consistent putter and one glorious sand wedge shot gave Nancy Lopez her second straight round of 70 and a one-stroke lead today in the U.S. Women's Open, one of the few tournaments she has not won since she joined the LPGA tour.

Lopez put together five birdies, including a spectacular chip-in from a bunker on the par-3 seventh hole, to fight off three bogeys on a scrambling sort of day at Baltusrol Golf Club. Her two-round total of 140 is four under par.

One stroke back were little-known Vicki Alvarez and a self-described beach bum, Janet Coles. Each shot a round of 69. They led the rest of a tightly packed field behind Lopez on Baltusrol's Upper course, an angular piece of artistry built on the side of a mountain.

Kathy Baker, a first-day leader with Lopez and Janet Anderson, shot even par to trail by two strokes in third place. She was followed at 143 by Sally Little, who shot a 70, and 1982 Open winner Anderson, who birdied the last two holes to finish with a 73.

Jan Stephenson, who was in second place with six others after the first round at one-under par, shot a 74 to fall five strokes back at 145. Hollis Stacy, the defending champion and three-time winner of the Open, shot consecutive 78s, missing the cutoff mark of 151.

There are two courses here, and the Upper course, where Tony Manero won the men's U.S. Open in 1936, is the lesser known. While this is the eighth Open to be played at the club (only the second for women), it is only the third, men's or women's, to be played on the Upper course.

But the Upper may require more putting skill to deal with the sloping greens, which resemble ski runs rather than putting surfaces. The trick is to get through the first six holes, which hang on the edge of Baltusrol Mountain, without falling off the side of the hill or knocking yourself out of the tournament.

Lopez may be the best putter on the tour, and it served her well on those testing greens. She sank birdie putts of six feet on the first hole, five feet on the fourth, and 15 feet each on the 12th and 16th.

"I had to work a little harder to shoot two under today," she said. "I was straying a little off the tee, but the putter was faithful. It kept me in there."

Lopez's birdie on the seventh hole may turn out to be the shot of the tournament. In a bunker to the right of the green, she blasted the ball out of the sand 20 feet and dead at the stick. It caught the top of the pin and dropped straight down into the hole as if on a string.

"I've never seen that before," she said. "It looked pretty funny. But I'll take it."

Coles had a bogeyless morning round that easily could have been in the lower 60s if not for an uncooperative putter. She missed a number of birdie opportunities on the front nine to remain at par at the turn.

"I missed all these putts real close," she said. "But to get off the mountain in even par is great. I told myself, 'Hey, pars are great,' and I didn't force it. I knew they were bound to go in sometime."

The putts finally dropped on the 12th and 13th holes, a pair of par 4s, for consecutive birdies. She had one more on the par-3 No. 15.

Coles, an eight-year veteran from Carmel, Calif., is ranked 33rd on the money list with $38,496 and has five top-10 finishes this year, including a tie for third at the United Virginia Bank Classic.

Something of a streak player, she was the last player to make the cut at the 1982 Open in Sacramento, Calif., but came back to tie for 21st. She had not been happy with her game lately and took two weeks off to regroup before the Open.

"I worked hard," she said. "I like to lie in the sun, I'm a California beach bum, but this time I sacrificed my tan for my golf game."

Alvarez has been grinding it out for seven years with relatively little success. She finally had some last year, with five top-10 finishes to earn $77,440. Her best this year was a tie for fourth at the Kemper Open in Hawaii, and she has earned $22,791.

Alvarez, the wife of a club pro in Jacksonville, has played more tournaments than any other woman on the Tour in the last three years, with 30 appearances in 1982, 31 in 1983 and 30 again last year. She has taken only two weeks off this season, playing 22 tournaments.

"I have a house to pay for so I have to keep playing," she said.

Alvarez started by birdieing the par-4 second hole with a 70-foot putt that broke three feet. She bogeyed the par-5 eighth to get back to par, but suddenly jumped onto the leader board with three birdies over the last five holes.

She birdied the 14th, 16th and 18th, hitting irons dead at the pin. On 14, a five-iron went to 12 feet; on the 16th, a six-iron rolled to six feet, and another five-iron on 18 stopped three feet from the hole.

"I've been playing well lately," she said. "But I haven't been scoring well, so this is a treat."

Baker, in her second year on the tour, is 26th on the money list with $47,792 and is one of the rising stars on the tour with four top-10 payoffs this season. She had a fairly consistent round of three birdies, including a 50-foot putt at the second hole, and three bogeys to remain one of the surprise leaders. "I think I'm in pretty good position," she said. "I'm open to anything."