Almost 8,000 woodworkers struck the Weyerhaeuser Co. today, shutting down the timber giant's logging operation and sawmills in Washington and Oregon in a strike that could turn long and bitter and drastically reshape one of the main industries of the Pacific Northwest.

The unions angrily rejected a "last and final" company offer in which woodworkers were asked to take pay and benefits cuts averaging $4.30 an hour.

"We're going to shut down everything that looks like there is a log going through it or to it," said Fid Lilly, an International Woodworkers of America (IWA) business agent at a Weyerhaeuser mill in Enumclaw, Wash.

It was the first major strike against the company in 20 years. The timber industry, which seemed to be recovering from seven years of distress in the national housing market, is watching to see if the strike spreads to 25,000 union workers at other Northwest timber companies.

The IWA and the Lumber, Production and Industrial Workers union have been operating without a contract since June 1, but they are bargaining independently with other timber companies, including Boise Cascade and Champion, which also are asking for pay cuts.

A last-minute attempt to avert the strike with federal mediation failed over the weekend. "We never really did get together," mediator Patrick Leyden said after listening briefly to the positions of both sides.

The depth of the woodworkers' anger began to show last week as wildcat walkouts hit several Weyerhaeuser plants in Washington.

"I've already lost my house," Brad Rhodes, a logger at a walkout site in Pe Ell, Wash., said of the on-again, off-again operations that have plagued the Northwest woods in recent years. "How is a strike going to hurt me?"

Workers are often laid off for extended periods, and average about nine months' work a year.

Unionized machinists struck a large Weyerhaeuser mill in Klamath Falls, Ore., Saturday night, and leaders of the woodworkers unions quickly supported that strike and directed their men to walk out today.

But the trouble in the Northwest woods runs deep. Foreign competition, high interest rates, the disappearance of easy-to-harvest old-growth timber and moves by some timber giants, such as Georgia Pacfic, into the lower-cost South have left the industry and the timber economy in disarray.

In recent years dozens of sawmills have closed. Unemployment runs above 20 percent in some areas. In 1979, when the decline started, burly loggers in the timber town of Willamina, Ore., were reduced to collecting ferns for Portland florists.

Many loggers have not returned to the woods, ending family traditions going back several generations to when the forests were the root of the Pacific Northwest's economy. The unions, whose membership is down 30 percent since the housing boom went bust in the 1970s, voted overwhelmingly to strike, and some workers say they will not return to the uncertainties of the woods.

But a Weyerhaeuser spokesman, James Bradbury, said the company could not remain competitive, with union members currently averaging about $20 an hour in wages and benefits (nonunion workers average about $12.50). He predicted more mill closures unless the unions accept the company's offer, which includes some productivity bonuses in good times.

The unions originally sought a 4.5 percent pay increase in each year of a two-year pact, but have backed off on that point.

Weyerhaeuser showed a $200 million profit last year, representing a 3.8 percent return on investment. Denny Scott, a spokesman in Portland for the woodworkers' unions, said profit projections for the company's wood products divisions were up 40 percent this year because of the turnaround in the housing market.

The picketing of Weyerhaeuser's 32 sawmill and logging operations began quietly, with the company shutting down. There were hints, however, that Weyerhaeuser will try to reopen. Bradbury said the company had no immediate plans, but reopening remains an option.

Scott warned that an attempt to break the strike could set off a powder keg among the already angry workers. Asked if this could mean violence, he said, "You bet."