If Mount St. Helens had been polite enough to file an environmental impact statement before it blew its top, regulators would never have given it a permit.

The monstrous black clouds that have been belching from the blasted north face of the volcano since Sunday are full of just the things the Environmental Protection Agency and the Nuclear Regulatory Commission are trying to control -- radioactive gases, sulfur dioxide, tiny dust Particles and other smelly pollutants.

The sifting, powder-like ash is clogging machinery in at least three states, covering crops and animals, and forming sticky goo wherever it gets wet. Its health impacts may be serious.

Mud slides have blocked waterways, clogged drinking water intake valves in Walla Walla, Wash., and halted shipping in Portland, Ore., and Astoria, Ore. As many as 35 vessels are trapped in the harbors. Enough trees were flattened to build 200,000 single-family homes.

Sunday's blast was at least equal to 40 kilotons of dynamite, more than twice as powerful as the atomic bomb that leveled Hiroshima.

"About 20 kilotons of force was contained underground in the volcano," said Dr. John Filson of the U.S. Geological Survey. "The rest of the energy came right up through the side of the mountain."

The agency estimated that the amount of material blasted loose over the countryside was one square kilometer of rock, ice and mud, or just slightly less than the amount of material from Vesuvius that covered the Italian city of Pompeii in 79 A.D.

At least three high-altitude sampling planes flew Tuesday and yesterday through the huge plume of dust, gas and ash as it drifted eastward with the high-altitude jetstream. One plane came out of NASA's Ames Research Center in California, another NASA plane came from Houston and a third plane flew out of Boulder, Colo., for the National Oceanic and Atmospheric Research.

They are trying to fill some of the information gap created when the Sunday eruption blew away most of the measuring equipment scientists had set up near the rim.

It is not yet known whether most of the gases and particles coming out now differ from those the mountain was spewing before the blast. A full report may take several weeks.

But Richard Perkins of the Battelle Research Institute at Hanford, Wash., said "hundreds of thousands of curies" of radioactivity, "far more than ever released by any accidental venting" of a nuclear power plant, have come out in the form of short-lived radon gas.

The gas is a byproduct of the decay of radium that occurs naturally in the earth's crust. Perkins said the estimate could be made from lead and other residues found in the grayish-white ash that fell to the ground in Washington four hours after the blast.

"There are always natural radioactive elements associated with volcanoes, but they are pretty insignificant" in terms of health effects, said Don Kelly of the geological survey's information office.

Far more worrisome, an EPA official said, is the ash, which has coated eastern Washington and much of Montana in dust two inches thick. Local drifts seven inches deep were reported in some areas.

Eastern Washington was already out of compliance with EPA dust standards before the volcano went, and this gift from Mount St. Helens has made EPA throw up its hands. "What can be done about it except pave the state?" said Robert H. Jacobson, EPA's regional spokesman in Seattle.

Officials are particularly concerned about the fraction of the ash that is in what they call the "inhalable range" -- fine enough to get pass the nasal filter hairs and membranes but not fine enough to be absorbed into the bloodstream. These particles lodge in the deep recesses of the lungs and often are not caught by the kind of surgical face masks people around the volcano have been wearing.

"We won't know how damaging it is until we know the chemical components," Jacobson said. Analyses so far have been contradictory, he said, showing different amounts of several components.

Among these are silica, feldspar, aluminum, iron and traces of zinc, manganese, boron, cobalt and molybdenum, all normally found in rock in the area and none considered harmful in ordinary dust, other EPA officials said.

The agency asked state officials in the path of the plume nationwide to monitor dust and rainfall continuously for any changes in it.

Sulfur dioxide, a product of burning carbon fuels and the main target of EPA controls on power plants, was coming out of the volcano at the rate of 10 to 20 tons a day before Sunday's explosion, about one-tenth of the amount emitted by a power plant that meets EPA rules. But the cloud is at least 100 times bigger now, observers said.

Sulfur dioxide is thought to be a major cause of acid rain, which kills fish and damages plants. Moisture at 300,000 feet inside the plume before Sunday was measured by the EPA at very acid levels reading 2.5 on the pH scale, where 7 is neutral.

But the leading edge of the volcano's breath passed over Virginia early yesterday, and scientists recorded no visible effect on the rains that drenched the area.