President Reagan dropped off in this economically depressed southern Oregon lumbering town today and blamed the recession on economic and environmental policies of the past.

Speaking to lumber company executives gathered here in the lunchroom of a Weyerhaeuser Co. plywood mill, Reagan acknowledged that the industry was hurting but predicted a "powerful and sustained" recovery accompanied by lower interest rates. In his weekly radio address, taped Friday night in San Francisco and broadcast today, the president made similar points and predicted that the unemployment rate also "will be heading downward."

Reagan's motorcade into Klamath Falls was greeted by groups of pickets bearing union signs and anti-administration posters. A large banner held by several protesters read, "You stay the course, we pay the price." Another placard said, "Reagan not welcome in Oregon."

Sources said Reagan had been given in advance seven or eight questions that would be raised by the panel of lumber company executives in prepared remarks and a subsequent question-and-answer session. Nearly all of the questions dealt with the recession and the prospects of recovery, and the president responded optimistically to all of them.

But he soon wandered off into the themes which frequently preoccupied him in past political campaigns when he was confronted with audiences of lumber and mining executives and other developers.

Denouncing "unreasonable" set-asides of land for public purposes, which he did not define, the president said that "the private sector has not been guilty of rape of all the natural resources" and added, "There is today in the United States as much forest as there was when Washington was at Valley Forge."

Reagan was sarcastic about some environmental claims.

"We have 80 million acres of wilderness land now," Reagan said. "This is land that you cannot have a road in or anything of the kind. It's there because out of the 250-odd million Americans in this country, we realize that at least 240 million of them are backpackers who want to hike into that wilderness area."

Warming to his pro-business theme, Reagan recalled the derisive ovation that Democrats had given him when he said in his State of the Union address that government has an important role.

"When I said that government has a part to play, yes, it does," Reagan said. "Government has a part to play by not doing the stupid things that it's been doing for so many years and by getting out of the way and getting off the back of business . . . . "

The last words of this sentence were drowned out by loud applause.

Oregon's unemployment rate was slightly higher than the national average when Reagan took office, and it has continued to grow during most of Reagan's term. The most recent unemployment figures show a slight decline in the jobless rate from 12.5 to 11.8 percent, still nearly three points higher than the unemployment rate which Reagan referred to as reflecting a "depression," when he was running for president.

The unemployment rate in the Klamath Falls area is between 13.5 and 14 percent, according to Oregon state officials.

Gov. Victor Atiyeh of Oregon, who met the presidential party here, was asked what Reagan would see on his quick stopover before returning from San Francisco to Washington.

"I don't know what you can see at a saw mill in 17 minutes," Atiyeh said. But the Republican governor congratulated the people of the area for working hard to obtain economic development and said he intended to "put in a word" for a timber industry relief bill to Reagan.

"Things are beginning to look better," Atiyeh said of the area's economy.

"When people start building, they start using lumber. It's still fragile. It's not solid, but it's moving in the right direction."

The Oregon trip was planned, according to administration sources, partly to give Reagan a forum to discuss economic recovery and partly to give the president's fellow Americans the impression that he has been doing more on his week-long trip to California than hosting Queen Elizabeth II.

On Friday, in San Francisco, Reagan made a speech strongly calling for free trade and increased exports, and his remarks were referred to favorably by lumber company executives today.