One of the most mysterious of all nature's rhythms -- the 11-year rise and fall of solar activity -- is rising toward a violent climax, and scientists say society has never been more vulnerable.

Since the last "solar maximum" in 1989, the networks of high-technology communications and satellites have expanded like condos on the beach -- smack in the path of the coming solar "storms."

Space station astronauts will be working in harm's way. And electric utilities are more reliant on cross-country transmission lines that can behave something like Ben Franklin's kites during big solar events.

Solar experts have predicted that the approaching solar maximum will be among the two or three strongest on record. Its main effects will be felt by July, peak early next year and end by January 2001.

"It could be an interesting few years ahead of us," said John G. Kappenman, of the Metatech Corp., a Duluth, Minn., engineering firm that helps companies brace for solar storms.

Significant solar eruptions have been on the increase for more than a year. Before they subside, they will unleash squalls of charged particles, hot gases and magnetic radiation.

Billowing across the solar system at millions of miles per hour, they will rattle the Earth's electromagnetic environment.

"We could start seeing an average of one per week as we get closer to the maximum," said Nicola Fox, a solar scientist at the Goddard Space Flight Center in Greenbelt.

The good news? People on the ground aren't directly threatened. The Earth's magnetic field and its atmosphere have shielded life here for millions of years. The solar maximum may even draw displays of the northern lights as far south as Texas.

It will surely be a bonanza for scientists, who have never been so well-prepared. A network of instruments on the ground and a constellation of orbiting observatories already are feeding them data.

"It's a very good time to be in the field," Fox said. The forecast events are part of the 23rd solar cycle observed since 1755. The recordkeeping began with counts of the dark spots -- sunspots -- that crowded the sun's face about every 11 years.

Jo Ann Joselyn, a space scientist at the National Oceanic and Atmospheric Administration's Space Environmental Center in Boulder, Colo., said this solar maximum is expected to be much like Cycle 22, which peaked about 1989.

A geomagnetic "superstorm" in March of that year triggered the collapse of the Hydro-Quebec electric power grid. Six million Canadians were plunged into darkness for nine hours.

The 24-hour storm triggered 211 power disruptions across North America and similar trouble in Scotland and Scandinavia, Kappenman said. It tripped circuit breakers and caused millions of dollars in damage to New Jersey's Salem nuclear power plant.

Four Navy navigation satellites were taken out of service. Another storm in 1991 knocked out Telsat Canada's $300 million ANIK communications satellite.

Scientists believe all these events have their roots in the sun's turbulent magnetic field. Like any bar magnet, the sun has north and south poles with field lines running between them. The lines trap ionized gas and charged particles such as iron filings.

The sun's rotation, and its roiling thermonuclear caldron stretch and twist the field lines. During a solar maximum, they become knotted and tangled like wound-up rubber-band engines. They poke through to the surface as sunspots or explode into the solar atmosphere.

Flares with the power of billions of Hiroshima bombs, and vast bubbles called coronal mass ejections, throw off gamma rays and X-rays, high-energy protons and electrons, and hot gas, some of it aimed toward Earth.

As these blasts run up against the Earth's magnetic field, or "magnetosphere," most particles are deflected like torrential rain around an umbrella. But Earth's magnetic umbrella is jostled and energized, producing what's called a "geomagnetic storm." Electrons trapped in the magnetosphere are accelerated through space, smacking into satellites, astronauts and the Earth itself.

Satellites accumulate electrical charges that can spark, damaging solar panels or other parts. Faster, high-energy particles may penetrate components and erase digital memory, scramble software or zap delicate computer chips.

Satellite makers fight back with shielding and backup systems, and operators can shut down vulnerable components. But Terrance Onsager, a plasma physicist at Space Environment Center, said much of what's in space today wasn't there in 1989. "We don't really know how it's going to behave under these conditions," he said.

When Panamsat's Galaxy 4 satellite failed in May, it silenced network TV and radio broadcasts, pager services and even credit card verification systems serving millions of Americans.

The outage was never officially explained. But Geoffrey D. Reeves of the Los Alamos National Laboratory is among many scientists who suspect space weather. Galaxy 4 failed during a powerful coronal mass ejection.

"Manufacturers get nervous when you point to this satellite and this event," Reeves said. "They're in competition and they have to be able to say their satellites are as good as, or better than the next guy's."

Manned spacecraft orbiting just a few hundred miles high are generally shielded by Earth's magnetic field. But their risks increase as their orbits approach the poles.

That's where the Earth's magnetic field funnels energized particles from the sun down to the upper atmosphere. The bombardment creates beautiful auroras, but human exposure can damage chromosomes and lead to cancer or death.

The international space station is being assembled in just such a northerly orbit. That makes it accessible to Russia's heavy-lift rockets, but its astronauts will face added risks.

Michael J. Golightly, chief of space science at NASA's Johnson Space Center, said that if the space station's radiation alarms are triggered, astronauts can retreat to several well-shielded modules.

But if body exposures approach dangerous levels, he said, "the decision has to be made: Is it worth the risk to keep them going longer, or do they need to be brought home?"

Expansion of the atmosphere due to heightened solar activity is expected to drag Russia's Mir space station to a fiery end this year. Other disturbances will disrupt shortwave radio signals and satellite navigation systems. Satellite phone systems, such as Iridium, may also be disrupted. "These guys are walking into a buzz saw," said Kappenman.

The electric power industry's increased reliance on long transmission lines and power transfers makes it more vulnerable, over wider regions, to the kind of geomagnetic storm that blacked out Quebec in 1989.

To defend itself, Hydro-Quebec spent $1.2 billion on protective hardware. Other utilities have made a less costly decision to develop improved solar forecasts.

NASA satellites now provide the Space Environment Center with at least a hour's warning of storms. The SEC then issues bulletins and alerts.

For solar and geomagnetic forecasts, see www.sec.noaa.gov or www.spaceweather.com.