ATWO-YEAR drought in the Pacific Northwest has reduced powerful white water rivers to a trickle, threatened the king salmon's migration routes to the ocean and shriveled orchards of red Washington State apples.

Turbines on huge hydroelectric dams no longer supply power surpluses for lack of enough free-falling water, and the great green forests of Oregon have become tinder boxes waiting for a match.Rainy Seattle has been stricken with good weather, ruining its image; and residents of San Francisco may see their lawns turn brown while water is rationed.

For the past two years there has been so little rainfall in the Northwest that key reservoirs are down as much as half. There has been so little snowfall that runoff from the spring thaw has brought little relief.

Although meteorologists differ, many say the cause of the disaster is "El Nino," a poorly understood weather phenomena that has left a strong ridge of high pressure poised over the Pacific Northwest for the past two years.

Because of the high pressure system, Pacific Ocean storms that normally barrel straight across the coast instead have been forced north into Canada and Alaska or south across Southern California.

In recent weeks experts say the El Nino has weakened, allowing storms to once again drop rain on the western sides of Oregon and Washington. The eastern sides of those states and northern California, however, remain victim to the weather ridge and there is little rain in sight.

As a result, water dependent industries are scrambling and some of the solutions are innovative.

Runoff in the mighty Columbia River system, for example, is expected to be 71 percent of normal his year. That reduction is expected to leave some critically low points.

For salmon migrating from their upriver birthplaces to the Pacific Ocean, the low water flows portend disaster the loss of as many as 90 percent of the migrating smolts but the Army Corps of Engineers has decided to truck many of the smolts past the low-water danger points.

The Bonneville Power Administration also plans special water releases in the Columbia in an attempt to protect young fish migrating downstream.

There is no remedy for the hydroelectric dams, however.

Low river levels have forced Bonneville to cut almost all spot power sales to California, reducing the BPA's revenue by some $300 million.

Agriculture also cannot be saved.

"The growers realize they have to live with what happens," says Chuck St. John of the Washington Apple Commission. "None of us knows how to do a rain dance or a snow dance. It's a cruel fact of agricultural life that nature holds the hole card."

St. John said without late season rains, Washington's apple crop the largest in the nation faces a disaster that can affect not only this year, but future years as well.

Farmers are facing possible restrictions on irrigation, and many have planted alternate crops that require less water.

In some cases, less water translates directly into fewer tourists.

The white water rafting season will be over earlier than normal this summer and has been canceled altogether on some rivers.

Jim Lethman, a Bureau of Land Management river manager in Medford, Ore., said that while his agency is gearing up for a big white water season on the Rogue River, many of the streams in northern California will have very short seasons due to

low runoff from the Sierras.

The river running season was canceled on the Owhyee River in eastern Oregon for the second year in a row, and there is no season on the Scott River in northern California.

Boaters and fishing enthusiasts will find low water levels in most reservoirs, with lots of mudflats and stumps showing.

Some communities in northern California face water rationing and restrictions reminiscent of the 1977-78 drought.

Forest fires are on everyone's mind.

"One of the most devastating consequences of the dry conditions in our state is a potentially hazardous fire season," California Gov. George Deukmejian said recently. "Already, there have been 1,200 wildland fires, 20 percent more than would be expected at this time in a normal year."

Deukmejian, known for tight-fisted fiscal policies, has approved an extra $10.3 million this year and next to hire more firefighters.

In the southern Oregon and northern California region hard-hit by fires last year, this is the fourth year of below-normal moisture and the second of severe water shortages.

Loggers are looking at reduced work time if high fire danger keeps them out of the forest. Employment figures show the average logger in Oregon worked fewer than 29 hours a week during September and October when forest fires closed the western Oregon forests.

Also, timbermen are seeing the first signs of long-term damage to the forests themselves as new seedlings wither in the dry earth and some older trees succumb to insects and disease.

Even a mid-April storm that dumped several inches of rain and snow in northern California could not take the edge off the fire season.

"What we call the heavy fuels, large logs out in the forest, are extraordinarily dry this time of the year," said Matt Mathes, a spokesman for the U.S. Forest Service. "We would need at least 6 to 8 inches of rain in a two-week period to change things significantly for the fire season."

The 1987-88 "rainy season" left California's Sierra Nevada only a small snowpack to melt into the reservoirs. By April, the lower mountains were so dry that further spring rain would mostly be absorbed.

Even with a mid-April storm, runoff of the Sacramento Valley watershed in the central part of California was expected to be less than half the average of 18.9 million acre feet. (An "acre foot" is the amount of water needed to cover an acre of land to a dept of 1 foot.) The record is 37 million acre feet, or 4.3 times as much as this year.

Among California's 900 water agencies, the severity of the shortage varies widely, and a few of the 151 reservoirs are still water rich.

The lack of bad weather has tarnished at least one city's reputation, and brought back bad memories in another.

Seattle's image as a rainy city suffered a severe blow last fall when it had to impose restrictions on lawn watering and ask restaurants to defer serving glasses of water unless asked.

Spring rainstorms finally brought enough precipitation to Seattle reservoirs to end the yearlong crisis. But, "We will continue to be watchful since there is still uncertainty about future weather and the possibility of returning to overly dry conditions," said Bob Groncznack, Seattle superintendent of water.

And in San Francisco, memories of the 1977-1978 drought are still sharp. Then, citizens cut down on flushing their low-water toliets, took showers together or at school or work, forgot about keeping their lawns green and washed their cars in secret if at all. Some restaurants cut down on washing by using paper plates.

Barring a miracle, water officials warn the same thing is coming up this summer.

Deukmejian already is urging conservation methods similar to those used in 1977, when California had 6 million fewer people, and has started citing suggestions from the "Urban Drought Guidebook," including repairing leaking faucets, using garbage disposals sparingly and washing only full loads of laundry and dishes.