Donald Berens has seen all the high points of America, from the snowy summit of Mount McKinley to the cattle trough behind Merrill Sterler's barn.

Berens is a "peak bagger," one of those restless souls in Vibram soles who are always looking for a new crag to scramble up and jot down in their log books. It's sort of a hobby, like stamp collecting.Last spring, Berens, a 38-year-old lawyer who lives with his wife and two kids in suburban Albany, joined an elite group of mountaineers who can boast of having bagged the highest peak in each of the 50 United States.

As far as those who keep track of such things can determine, he's the seventh person to do it.

Jack Longacre, a 50-year-old trailer park proprietor in Mountain Home, Ark., claims to be the sixth person to climb the high points. He says he knows of about two dozen others who are working on it.

It's an arduous task, with many obstacles to overcome. In Alaska, there are blizzards, crevasses, pulmonary edema. In Delaware, there are speeding cars. In Indiana, the high point is obscured by cornstalks.

It took Berens 21 years, but he bagged them all. He jotted the last one in his log book on May 27, 1987, when he trudged through thigh-deep snow to reach the supposedly desert summit of 13,143-foot Boundary Peak in Nevada.

"When we got to the top, we celebrated with champagne and fruitcake, and just contemplated our situation," he says.

Berens, who works for the state attorney general's office, traces his zeal for hiking back to when he joined the Boy Scouts in suburban Rochester.

"I got my first state high point when I was a senior at Pittsford High School," he says. That was New York's 5,344-foot Mount Marcy.

Berens got his second high point, Mount Greylock in Massachusetts, when he was a student at nearby Williams College. He climbed Vermont's high point, Mount Mansfield, while visiting an uncle in Burlington.

"At that point I had three," he says, "and I realized I only had 47 to go." Somehow it just snowballed from there.

The major obstacle to climbing all the high points, besides having the time and money to travel all over the country, is that some require technical rock and ice-climbing skills. Realizing that, Berens enrolled in a course at Rainier Mountaineering Inc. in Seattle.

In 1975, he climbed Washington's high point, 14,410-foot Mount Rainier, under the guidance of two premier mountaineers: Phil Ershler, who in 1984 became the first American to reach the summit of Mount Everest via the north face, and Marty Hoey, a young woman who died on Everest's north face in 1982.

The most challenging of the high points was Alaska's 20,320-foot Mount McKinley, the highest summit in North America. It took a 17-day expedition to get to that summit, Berens says.

"We had to wait out a two-day snowstorm at 14,000 feet," he says. Because of the thin air, one woman in the group developed pulmonary edema, a flooding of the lungs with fluid.

But Berens recalls the experience fondly. He says McKinley was one of his favorite climbs because of the fellowship among the climbers, the sense of accomplishment, and the starkly beautiful scenery.

"Each region is beautiful in its own way," Berens says. "Kings Peak in Utah has beautiful meadows and forests which McKinley doesn't have. Granite Peak in Montana has sharply defined silhouettes, cleanly fractured granite with lots of angularity."

The ugliest high point, he says, was Clingman's Dome in the Great Smoky Mountains in Tennessee. "There's an asphalt sidewalk all the way to the top," he says. "It's so crowded, you don't get any sense of isolation or accomplishment."

The most dangerous high point to stand on, he says, is the one near Wilmington, Del. "That's because the high point of Delaware happens to be the double yellow line of a road that goes over a hill."

The lowest high point is an unnamed hump in the Florida Panhandle, 345 feet above sea level. "It's a scrubby little hill covered with short pine thickets," Berens says. "It's kind of hard to tell which point is the highest, so I just wandered around until I was convinced that I'd stood on every little nubble."

Berens says finding some of the high points would be nearly impossible without the help of a little guidebook written in 1970 by Frank Ashley and published by La Siesta Press in California.

But the book itself is hard to find.

"It's been out of print for 10 years," Ashley said in a telephone interview. "There's not much interest in doing the high points. It takes a lot of time and money."

But Longacre says he thinks interest is growing. During the four years it took him to do the high points, he says his curiosity was piqued by notations in the sign-in books on some of the summits.

"I read it again and again: This is my sixth, my twentieth," he says. "I was curious to find just how many people were doing this." So he put an ad in the back of a mountaineering magazine with his address, asking people who were doing the 50 to write to him.

"I'd like to get some kind of an organization going," he says. He corresponds with about 20 people who share his interest and occasionally puts together a newsletter.

Longacre also keeps track of new surveys which have changed some of the official high points since Ashley wrote his book.

Berens discovered after he climbed 1,979-foot Mount Curwood in the Upper Peninsula of Michigan that the U.S. Geological Survey had determined another hill a few miles away was a foot higher. Last spring, he got together with some other people who were aspiring to do the 50 and climbed the new high point, Mount Arvon.

He discovered another new survey when he happened across a National Geographic article that said Iowa's high point was no longer 1,631-foot Ocheyedan Mound in the northwest corner of the state, but a slightly higher spot on the farm of Merrill Sterler near Sibley.

Last spring, Berens found the general area on a topographical map, and then drove around until he saw a mailbox with the name Sterler.

"The Sterlers were very kind and gracious," he says. "They gave me permission to go on their land, and even gave me a postcard showing their high point."

"We get quite a few people coming out here to see it," Donna Sterler said in a telephone interview. "There were about 10 or 12 this summer."

The high point is out in back of the barn, she says, near an old cement cattle trough. The Sterlers boast of the distinction bestowed upon their farm with a license plate on their pickup truck reading "High Point."

Berens actually spent less time hiking than driving, sometimes for thousands of miles in a peak-bagging swing through the Great Plains, the Dakotas, or the South.

"One thing that I've learned from this experience," he says, "is an appreciation for the geography and the people all over the United States. There are some places that I know I'd never have visited if not for the fact that there was a high point there."