Mount St. Helens erupted today with the greatest force since it blew its top a week ago, spewing ash and debris 40,000 feet high and sending a black, gritty ash cloud toward the heavily populated areas of western Washington and Oregon.

It was the second Sunday in a row that the mountain erupted violently. Its May 18 eruption, packing the violence of a 10-megaton bomb, took more than 1,300 feet off the top of the once-conical peak, and left 23 known dead, 76 missing, about $1.5 billion in property damage and much of eastern Washington covered in ash.

Today's eruption, occurring at 2:36 a.m. PDT, appeared to be less serious. But wind and weather conditions combined to blanket new areas of Washington and Oregon with muddy ash, forced the evacuation of mountain and river valley towns and set off flood alerts along four southwestern Washington rivers.

No deaths were reported today, but communications were hampered by overloaded telephone lines and electrical power outrages in wide parts of Washington State as the ash fell throughout the day.

Unlike last Sunday,when the volcanic ash drifted eastward, over sparsely populated areas, today's winds were carrying a large cloud toward major population centers, including Portland and Seattle.

Washington Gov. Dixy Lee Ray issued an executive order barring anyone from approaching nearer than 20 miles to the volcano. Earlier, she had established the "red zone" at five miles. Unauthorized persons in the danger zone face fines of $1,000 and a year in jail.

The government's order forced the evacuation of two mountain towns, Cougar and Yale. The seething mountain also closed or restricted operations at airports in Washington and Oregan, and effectively shut down an interstate highway and nine state highways.

Reports showed the new ash cloud extended northwest from Mount St. Helens to Olympia, the Washington state capital, and southwest to Eugene, Ore., and some nearby Pacific coastal towns. Ash also was reported in Bremerton, Wash., 10 miles across Puget Sound from Seattle.

Like a rerun of last weekend's day-into-night ash storm over eastern Washington, residents of the western part of the state saw their morning turn pitch-black and remain that way until almost 10 a.m.

"It was dark, black until about 9:30." said Lorraine Robinson a representative of the Washington State Civil Air Patrol. Electricity went out as wet ash fell in Longview and Kelso, two southwestern cities that have served as evacuation centers for flood victims from the first eruption.

Dwight R. Crandell, volcano coordinator for the U.S. Geological Survey, said in Vancouver that the latest eruption surprised scientists and that it was too early to tell what it meant about future activity. He said, however, it was unlikely there would be a lava flow.

Crandall said he stood on "the outer flanks of the volcano" Saturday and saw nothing to indicate that an eruption was impending.

Even when ash and steam burst from the gaping crater to heights of 11,500 feet Saturday afternoon and to 20,000 feet Saturday night, he said, scientists had no reason to suspect a major eruption was in the making.

Three minutes after this morning's eruption, the ash and stream plume had reached 24,000 feet and looked like "a dark blob, settling on top of its own ash cloud," according to Tim Hait, a scientist for the geological survey. o

The eruption triggered a major mud flow on the north fork of the Lewis River on the mountian's southeast slope. That river leads into a series of reservoirs and dams that eventually empty into the Columbia River. The mud flow reportedly halted without causing major downriver flooding.

Hait said the new material coming out of the mountain was pyroclastic, hot magma from deep inside the volcano and similar to the material the mountain vented a week ago. The eruptions were coming from two vents, one on the northeast corner of the new crater and the other at the southwest corner. This was the first sign of any major volcanic activity on the south side of the mountain.

Hait, who said he believed the ash emissions could continue for years, also said it was possible the mountain would begin spilling "mild" lava flows. But he added he was reluctant to make "any prediction as to what will happen next."

Doctors have reported an outbreak of illnesses with symptoms of headaches and diarrhea among residents, mostly in eastern Washington where the ash fell last week. Dr. Denis Prager of the White House science office said the illnesses connected to the ash fall would probably be minor or short term.

But long-term exposure to the ash could lead to more serious ailments, including emphysema and bronchitis. Bob Jacobsen, a spokesman for the Environmental Protection Agency, said. Such ailments, if they do come, would appear only after "considerable exposure" and wouldn't show up for five to 10 years, he said.

The new eruption stranded thousands of Memorial Day weekend vacationers, many of them at coastal resort towns cut off by what state police described as "extremely hazardous driving conditions" -- rain mixed with ash to form a grimy mud.

Most highways in the area were closed and the Washington State Patrol asked tourists to "stay put" and not attempt to return home. Patrolmen were turning back motorists as they attempted to enter Interstate 5, the main highway between Seattle and Portland.

Along I-5, motorists were clustered around closed gasoline pumps, filling their window washing tanks instead of their gasoline tanks. Early in the morning, a police officer said, driving 10 miles required two tanks of window washing fluid.

Cars, apparently stalled out by ashclogged air filters, sat abandoned along the stretch of the interstate from Portland 45 miles north to Longview.

At the Red Cross evacuation and refugee center at the Cascade Middle School in Longview, some weary families were becoming frustrated and hostile after a week of being shuttled back and forth between their homes and the makeshift camps.

Tom nelson, a supervisor at a Weyerhaeuser timber camp where five people were killed a week ago, stood with his wife, Charlotte, amid the disarray of the evacuation center. They had been brought there for the fourth time in a week by today's eruption.

"Why don't they just take a couple of jets and bomb the mountain?" Nelson said. "Then the mountain would collapse on itself and this thing would smother. How long are we going to live under the threat that it might go?"

Pat Cruzan, a supervisor for an oil company, has been evacuted to Longview from his Toutle River Valley home four times because of the threat of flooding from a mud dam the volcano created on devastated Spirit Lake.

The 10-mile-long artificial dam, which is holding back water that reaches 200 feet deep, has been closely watched by authorities. It appeared unchanged after today's activity.

But Cruzan believes "they should bring a demolition expert in here and blow that dam and let the water go. That's what keeps us going in and out, the threat of this wall of water coming through."

Cruzan's wife, Marge was driving to work at 5:30 this morning when the ash began to fall. "It was terrifying," she said. I don't know what made me keep going. You put out your hand and it would get filled with little black dots of mud."