OCKELBO, Sweden (AP) _ Two weeks of skiing, boating, fishing or hiking in an unspoiled forest of pine and birch.

That's what Sweden's National Prison Administration offers as a vacation for hardened criminals serving prison time.

The vacationers at Gruvberget, a former logging camp 125 miles north of Stockholm, are convicted murderers, rapists, drug dealers and other felons serving long-term sentences.

''We have the lowest walls of any prison in the world, but they are also the thickest,'' said director Rolf Johansson, referring to the 12 miles of hilly woodland to the nearest farm.

Up to 30 prisoners at a time stay at the mountain retreat for two weeks, many with their wives and children. Prison officials number three, and none have weapons.

Sweden has one of the world's most liberal corrections systems; prisoners are called ''clients,'' furloughs are frequent and the accent is on rehabilitation.

''We want to give clients the opportunity to meet their wives and children outside the walls of prison, and to give them new ideas about life,'' said Johansson.

''This is a great place,'' said an American doing time for selling drugs. ''I've been learning cross-country skiing. Yesterday we went walking seven or eight kilometers (four or five miles) in the woods and had a cookout - hot dogs.

''It's like a real vacation. It's helping us re-cement our relationship,'' he added, nodding toward his Swedish wife. The 45-year-old former social worker refused to give his name. ''Just call me Jack, OK?'' He said he was a Vietnam deserter and has been in Sweden for 20 years.

After completing one-third of their terms, prisoners are eligible for furloughs of up to 48 hours as often as six times a year. Most prisons have conjugal rooms for visits from wives or girlfriends, and marriage is not a visiting requirement.

The furlough system was curtailed for a time after the escape in October 1987 of one Sweden's most notorious spies, Stig Bergling, who apparently slipped out of the country while home on a weekend furlough.

The prison service reported 287 cases of prisoners returning late or drunk from the 8,951 furloughs granted in 1987, the latest year for which statistics are available. About 15,000 people were sentenced to prison that year, 8,000 to sentences of less than two months, and 1,500 for more than one year.

No one has ever tried to escape from Gruvberget. The guests are given train tickets at their home prison and make their own way to the village. Since most are nearing parole, Johansson said, it would make little sense to jeopardize the release.

One recent day, skis were propped against the wooden two-story cottages, which were built in the 1950s for woodcutters and their families.

Four men in jeans or jogging suits were lazing in winter sunshine. Two were with their wives, and children were crashing through the nearby woods. They were waiting for a gray prison bus to take them to a public ski slope about a half-hour away.

The Prisons Administration bought the village 27 miles from Ockelbo, the nearest town, in 1968. A full-sized basketball gym and a small dining hall were added to the 22 existing buildings, including the loggers' cabins.

It took four years before the authorities could override the skeptics and invite the first group of prisoners, Johansson said.

Neighboring villages ''were a little worried when we started,'' Johansson said. ''Over the years they got used to us.''

About 1,100 prisoners a year spend time at the vacation camp. About twice that number apply, Johansson said. They are selected on the basis of good behavior and a clean record on previous furloughs.

Each two-week session is built around an activity theme. One popular course is ''dance and exercise,'' in which the prisoners do physical training, aerobics and learn ballroom dances.

Johansson said religious classes are often requested by men convicted of murder or manslaughter. Other sessions feature seminars in family life or resisting drugs.

''Mainly we try to teach them basic things: to cook, to dance or to walk in the woods with their children, which they have never done,'' Johansson said.

For the prisoners, furloughs and the special experience of Gruvberget are lifelines to the world outside the walls.

''If I couldn't see my wife on the weekends, be with the kids a couple or three hours a week, be able to touch them, I'd lose contact with life,'' said Jack the American.

''In the States, if you get six years you'll sit for four, five or maybe all six,'' he said. ''And conjugal visits? Forget it. But that's what holds families together. If you have that kind of contact, you can get back into life again.''