Crime, often committed by bands of hardened urban criminals, is becoming increasingly commonplace in the once-serene national parks of the West, according to law enforcement officials of the National Park Service.

Even in such a spectacular locale as Yosemite National Park in California, groups of what are known as "car clouters" have been found moving through crowded campsites and trailheads, seeking loot from campers' tents, cars and recreational vehicles. A few of these criminals, according to some rangers, are traveling from park to park, attracted by what one ranger called "the real easy pickings."

"There are a lot of professional criminals who come here to prey on all the campers," said Yosemite's Lee Shakelton, chief law enforcement ranger for the 760,000-acre park. "They can get away with it because of all the crowds here. Sometime we can have as many as 20,000 people at one time in Yosemite Valley and that makes it real easy for them."

Like many national parks, Yosemite has had a large increase in visitors in recent years. In 1966 more than 1.8 million people went to the park; 10 years later the number was more than 27 million. Far outstripping the rate of increase of visitors, however, was the rise in the rate of arrests for felonies. Over those same years such arrests more than tripled, going from 250 to 870.

The pattern at Yosemite is common throughout the entire 298-park, 35-million-acre national park system. In the 10 years between 1967 and 1977, for instance, the numbers of visits paid to the parks increased from 139 million to 261 million. But the crime rate over those years rose, even faster, according to U.S. Park. Police Maj. Jacks Sands, going from a 1967 figure of 3,400 major crimes - including homicides, rapes, burglaries, larcenies and car thefts - to more than 7,7000 last year.

Law enforcement officers like Shakelton view the increasing crime rate as a symptom of what he calls "the urbanization" of popular parks. "It would appear we're getting more of the urban feeling coming into the valley now where we used to just get the outdoormen type of thing," Shakelton said. "I guess these city folks have just a different life style."

Shakelton expects the crime and visitation rates to increase, perhaps to record levels, by the end of summer. The situation was particularly bad during the recent Fourth of July weekend when rangers in Yosemite made 34 arrests, 11 for felonies. At the end of the four-day holiday the Parks 16-bunk jail, completed in 1974, was so crowded that some prisoners had to sleep in the holding cell.

They Yosemite managers are particularly worried about the presence of bands of "car clousters," some of whom, he says, are now working all the parks along the mountainuous spine of California from the Sierras outside Sacramento to the San Fernando Mountains southeast of Los Angeles, a distance of well over 400 miles.

Such organized criminal activity has also been by rangers in such locales as Yellowstone National Park in Wyoming. Jerry Phillips, assistant chief manager in charge of Yellowstone's law enforcement says that as many as 200 to 250 vehicles have been "clouted" in the park annually in recent years. One group in believed to have hit as many as 25 parks.

One prime attraction for these groups, Phillips believes, is the attitude of trust most visitors still bring with them into the parks. "People have traditionally felt safe in the park," Phillips said. "They leave their gear in their cars and go up in the hills and come back in a few days and expect it to be there when they get back. It's sad to say, but the parks are like anyplace else these days."

To combat the crime problem, the Park Service has been retraining rangers in law enforcement tactics since 1971. In 1976 such training became mandatory for rangers seeking law enforcement powers, and to date some 1,100 rangers have completed the necessary police training.

Yet, despite these moves, many chief law enforcement rangers in the busiest parks say that, because of stricter training standards and budgetary restrictions, there are actually fewer rangers with police powers on the line now than in recent years. In Yosemite, for instance, the number of law enforcement personnel has plumeted from 110 last year to 75 this summer, and at the 1.4 million acre Lake Mead National Recreation Area in Nevada, it has dropped from 44 to 38.

While Park Service spokesmen in Washington are unable to give total figures for law enforcement personnel nationwide. Lake Mead chief ranger Newton Sikes says such drops in ranger personnel are commonplace throughout the system and are threatening the safety of parks visitors.

"We don't even have been enough people to patrol the nights as well as the days." Sikes said. "The thieves have found this real easy pickings. Our crime rate keeps going up and our rangers just can't keep place."

Several top rangers blast the Park Services national leadership and the Interior Department for what they see as a refusal to come to grips with the need for more policing in the parks, has the situation well in hand and accuses some rangers of being a little too eager to change the nature of the parks.

"I know a lot of people in the service disagree with us," Wilson said, "but we feel you don't need a 357 magnum on every ranger for the people to have a good time. Remember our job is to make sure people have a pleasant experience in the parks. We don't want to set up a police state - that's not why we're here."