President Carter flew over the barren landscape around Mount St. Helens today and said the devastation caused by the eruption of the volcano was 'the worst thing I have ever seen."

Skirting as low as 200 feet off the ground in a Marine Corps helicopter, the president flew across miles of a bleak and colorless wasteland of ash, mud and silt that was littered with the remnants of thousands of trees, stripped of their foliage and lying like broken matchsticks in the grime.

"Somebody said it looked like a moonscape," Carter said here after the 30-minute flight above the most devastated areas around the Mountain. "But the moon looks like a golf course compared to what is up there. It is a horrible looking sight."

At a news conference in Portland after the tour, the president pledged that whatever assistance is necessary will be provided to the stricken area. But he left the Pacific Northwest later today without making any specific commitments of federal funds and other aid.

Carter said he could not estimate the ultimate cost of the disaster to the federal government, but that it will be "of such a magnitude" that it will require a special appropriation by Congress.

Low-lying clouds and swirling sleet and snow prevented the president from getting close enough to see Mount St. Helens, the Cascade Range peak that exploded Sunday morning, transforming the lush, green countryside around it into miles of gray and lifeless rubble. But he saw enough during the day to speak in awestruck tones about the experience.

"There is no way to prepare oneself for the sight we beheld this morning," he said at the Portland news conference.

Earlier, standing in a cold rain in Kelso, Carter told reporters:

"I don't know if there is anything like it in the world. There's nothing left by massive piles of mud and what used to be mountain . . . It's an unbelievable sight. There is nothing like this in the world."

Accompanied by federal, state and local officials, and a large press contingent, the president left the Portland airport early this morning at the head of a fleet of eight Marine Corps and Army helicopter.

The helicopters flew first along the Columbia and Cowlitz rivers, and for miles the landscape below was peaceful and green, covered with towering fir trees that give Washington its nickname of "The Evergreen State."

Over Kelso and its neighboring city of Longview, the river waters were a rich brown, clogged with silt that has flowed downstream from the devastated mountainside to the east.

The flet of helicopters approached Mont St. Helens along the north fork of the Toutle River, and gradually the extent of the destruction became evident.

The green landscape turned to gray as the president flew over trees, still standing, but caked with ash from the eruptions. Closer to the site of the explosion, miles of trees lay broken in mud. In some sections, tree stumps scattered amid deep mud and water-filled craters were the only sign of what last week was a dense forest. Roads in the area were layered with mud and ash. There were no signs of life.

According to helicopter pilots, Carter came within three miles of the summit of Mount St. Helens and four miles of Spirit lake, where receding waters have lessened the danger of downstream flooding. But the clouds obscured the mountain, and when the rain turned to sleet and snow, the helicopters turned back.

"When the helicopter pilot decided to turn around, I did not argue with him" the president said later.

A small crowd at the airport here applauded when Carter, dressed in a blue suit, tan raincoat and thick-soled work shoes, stepped off his helicopter into the cold rain.

He went from the Kelso Airport to the Cascade Middle School, which is serving as an evacuation center for 47 refugees from the volcano area. The president walked through the center, chatting and shaking bands with the people gathered there.

The chief concern of state and local officials here is the massive cleanup job the face and the devastation to the economy of the region. Carter has already declared Washington a major disaster area, making residents eligible for special federal assistance.

And he said today he will make similar declarations for other states, probably Montana and Idaho, which are suffering from the ash fallout from the eruption.

But Washington Gov. Dixy Lee Ray, who, along with Idaho Gov. John V. Evans, accompanied the president on the flight, said the volcanic eruption was "a unique type disaster and we need much more than that."

Forest Service officials continued to agonize over the fate of the billion board feet of lumber reduced to neat rows of matchsticks by Sunday's blast. Chances for its salvage depend on whether access to it becomes available before the wood begins to rot.

The ash coating the trees will be a problem in any removal effort and for washing and sawing equipment, if the trees get that far. Dead animals in the flattened forest will further complicate matters.

Officials caution that damage estimates are preliminary, but it is thought that more than $200 million worth of timber is involved.

At the Portland news conference, Carter said it will be years, possibly decades, before the damage caused by the eruption is overcome. He promised to "work very closely" with state and local officials "to try to decide how to allot responsibility, how to make arrangements for meeting the heavy financial costs and how to schedule these efforts with the maximum involvement of the general public."

The president said that fears of severe health and environmental dangers in the area around the immediate blast sight have lessened considerably.

Carter even appeared to find a bright side to the disaster that has struck this area. When access to the Mount St. Helens region can be restored, he said, "This will be a sight that people will come from all over the world to observe.

"The impressiveness of the force of nature is overwhelming," he continued, "and when places are fixed for tourists and others . . . I would say that it would be, if you will excuse the expression, a tourist attraction that would equal the Grand Canyon or something. It is an unbelievable sight."

White House officials have dismissed out of hand suggestions that the president's hastily arranged trip here was largely a media extravaganza designed to show presidential concern for the West Coast before the California presidential primary on June 3. Asked today what the value of the trip was, Carter stressed that he could not have imagined the extent of the devastation and said this will help him and other federal officials in dealing with the aftermath.

Meanwhile, according to the Associated Press, the toll from the Mount St. Helens eruption threatened to climb far beyond the 15 confirmed deaths as officials searching for bodies said that there had been sightings of perhaps 15 more.

At the same time, the number of those missing dropped to 73 as geologists flew into the bowels of the volcano to find a "scary and spooky" crater nearly a mile deep.

Seismographs on the volcano detected new "seismic noise" between 5 p.m. Wednesday and 1 a.m. today.

Seismologist Craig Weaver at the University of Washington, where the noise was recorded, described it as similar to a harmonic tremor, which indicates the movement of molten rock within the mountain.

But Tim Halt, a scientist with the U.S. Geological Survey, said the seismic noise should not be taken as an indicator that molten rock was moving or that another eruption is coming.

Halt also reported, "The mountain is intermittently and vigorously steaming to 13,000 feet."

One shallow earthquake, greater than 3.0 on the Richter scale, was reported about 5 p.m. Wednesday, Hait said. A deeper quake measuring 3.6 occurred at 9:25 p.m.

Meanwhile, engineers at the Trojan nuclear power plant, 40 miles north of Portland, Ore., reported that the unit has been shut for refueling since well before Sunday's eruption and had been scheduled to remain closed until mid-July. Cooling water intakes on the mud-choked Columbia River were shut off when refueling began and the plant has been maintaining itself on recirculated water, according to a spoksman for the Nuclear Regulatory Commission. "There has been no effect on plant operations," the spokesman said.