If there is a chink in President Reagan's western armor, it is called Oregon.

More than anyplace else in the West, concern about the economy, disagreement with his environmental and defense policies and distaste among moderate Republicans and independents for the right-wing clerics congregating under Reagan's banner make the president potentially vulnerable here.

But even in this state, where former supporters of 1980 independent presidential candidate John B. Anderson and 1984 Democratic primary winner Gary Hart express strong distaste for Reagan, the president has an ace in the hole: the unpopularity of Walter F. Mondale as an alternative.

"We're having a negative election," said Tim Hibbits, a highly regarded Portland pollster. "Reagan has only a 52 percent approval rating here, which normally would make him a very vulnerable incumbent. But Mondale is in worse shape when it comes to negatives."

Mondale told Oregon campaign aides after a visit here last Wednesday that "if I don't carry Oregon, I'm not going to be in the national race." Craig Berkman, a major Republican fund-raiser, said, "This is a tough state." But he added that if Mondale carries only six states, Oregon would be one.

However, Hibbits said, Mondale was 22 points behind in a statewide poll he took the week after anti-Mondale speeches from the Republican convention had dominated television. "But it's been coming down steadily," he said, "and I would bet this state will be in the 52 to 53 percent range."

In 1976, Jimmy Carter missed carrying Oregon by less than 2,000 votes and in 1980, Reagan won by almost the 10 percent of the vote siphoned off by Anderson in his third-party bid.

Today, the leaders of that Anderson effort, and perhaps many of his followers, are leaning to Mondale, despite serious misgivings.

Anderson's 1980 Oregon chairman, one-time state attorney general candidate Lyndon (Tuck) Wilson, is a self-described "Rockefeller Republican" who has "watched with dismay my party's drift to the right."

Over coffee, he ticks off his disagreements with Reagan, ranging from the environment ("We haven't forgotten James Watt out here") to the school-prayer and abortion amendments. He also mentions the budget deficit and interest rates, a sensitive subject in this timber and wood-products state, where persistent problems in the housing market have left unemployment over 9 percent. But even with these disagreements and with Anderson's decision two weeks ago to endorse Mondale, Wilson has a hard time swallowing the Democratic challenger.

"The trouble with Mondale," he said, "is the Carter hangover. He's not come clearly into focus for me. I still think of him as Jimmy Carter's vice president."

Wilson added that he was distressed by "what I regard as Mondale's protectionist policy on trade," and "even though I think his approach to the deficit problem by raising taxes is much more realistic than Reagan's, I can't help remembering that the Democrats created the original deficits by ministering to their constituencies."

"If there is a tie-breaker for me," Wilson said, "it's got to be the international policy." A supporter of a nuclear weapons freeze, like most Oregon voters and politicians of both parties, he said Reagan appears to him as a "man who has heightened Cold War tensions just to justify his defense-spending policies . . . . He's fanned that hysteria."

Republican candidates have carried Oregon in seven of the last eight elections, but the state has a tradition of progressive Republicanism. The two GOP senators, Mark O. Hatfield and Bob Packwood, have been frequent critics of Reagan, and Republican Gov. Victor Atiyeh, though more conservative, has been outspoken in saying Reagan should be giving top priority to reducing the deficits which, Atiyeh says, are at the root of Oregon's economic problems.

The progressive Republican tradition created the climate in which Anderson got a 50 percent bigger chunk of the vote in Oregon than nationally. And the national GOP's recent focus on conservative social policy issues has added to the strains for Reagan supporters in Oregon.

State Rep. Mary Alice Ford, former Republican chairman in suburban Washington County -- one of the more affluent and pro-GOP parts of the state -- was a vocal dissenter on the Platform Committee in Dallas.

Though she backed Reagan over President Gerald R. Ford in the 1976 Oregon primary and remains loyal to the GOP ticket, she worries that the Democrats will "pull a lot of votes on the feminist and social policy issues" in her county, populated by young high-tech families.

Asked what Reagan could do to help himself, she said bluntly, "He could get off that school-prayer amendment. People here don't want us mixing religion and politics. The question I've been asked most is, 'Why did you people let Moral Majority leader Jerry Falwell take over your convention?' "

Diana Wilson, head of the Reagan campaign in Oregon, said cautiously that "I can't tell yet" how much impact the platform will have. "Some people are very unhappy with some parts of it," she said, "but for most, I don't think it will diminish their support for the ticket."

It did decide Ron Schmidt, however. Formerly press secretary to the late maverick Republican governor, Tom McCall, and now a successful Portland business and political consultant, Schmidt voted for Anderson in 1980.

For the first time, he is publicly supporting a Democrat, Mondale, "because of the Republican platform and the clear message from Dallas that the born-again element is taking control of our party."

"I just feel much more comfortable with Mondale and vice-presidential nominee Geraldine A. Ferraro," Schmidt said.

Comfort is not the quality many voters derive from Mondale, however. Real estate developer Scott Montgomery, who joined Wilson and Schmidt in the Anderson campaign, said Mondale "doesn't give me much of a choice. I have no confidence in him or Reagan. I have an absolute terror of what Reagan may do to the economy, with his cavalier attitude on the deficits. We went through three years of hell in this state and it could be worse in a second term.

"At the same time, Reagan is a known quantity. And I don't feel like I know Mondale at all. If I were forced to make a choice, I might stay with the evil I know."

Pollster Tibbits said Mondale's negatives began to grow in Oregon during the late winter and early spring primaries in the big eastern industrial states such as Illinois, New York and Pennsylvania, where Mondale fought off Hart's challenge.

"I don't blame him for doing what he had to do," Hibbits said, "but when he went to his labor and constituency-group base in those states, he really turned off the independent Democrats and ticket-splitters in this state. He put himself in the corner of old-style politician."

Ferraro has helped him climb part way out of that hole. Her selection was popular with the pro-Hart convention delegates, reflecting a state where women candidates fill half the top ballot spots this year. Ferraro's appearances in Eugene and Portland have drawn big crowds.

Mondale has begun to win some leadership support. Karen Alvarado, coordinator of Hart's primary campaign, met Mondale for the first time at a private discussion before a Portland rally last Wednesday and was surprised to find him "so impressive in that setting. His voice sounded about two octaves lower than it does on television . . . . I feel a lot better about working for him."

But among the swing voters, Mondale still has great doubts to overcome. In two days of interviewing at the Washington Square shopping mall, a cross-section of the ticket-splitting suburbs, there were frequent examples of Reagan critics who are unimpressed by what they have heard so far from Mondale.

Retired Beaverton factory worker Jack Hemphill voted for Reagan last time "because of inflation," but has decided "he's all for the rich. I wouldn't vote for him again if there was any other choice. But Mondale just seems very poor to me."

Forest Grove firefighter Jesse Martinez, 29, voted for Reagan last time but worries about "the lack of jobs for people my age." But he said that "Mondale would make a lousy president -- he's too wishy-washy. He couldn't make a decision if he had to. The Russians would love to have him in office. They know they can't walk all over Reagan the way they could with Mondale."

Asked about his reaction to Ferraro, the fireman said, "I might have voted for the Democrats if she were the candidate for president. She's different."

Marcia Stewart, a nurse with two young children, has a different foreign policy perspective, finding Reagan "frightening in his lack of concern about nuclear war" and an "anti-feminist elitist," to boot.

She voted for Carter last time and will support Mondale, but he gets no respect with her vote. "He's very weak. All his talk is just rhetoric. Ferraro just outshines him when they're together, which is kind of too bad."

Janet Bjork, a Warren housewife, articulates the dilemma of the undecided voter as well as anyone. In 1980, she voted for Carter because "Reagan seemed like he could get us in trouble, the way he was shooting off his mouth" on foreign policy.

But she said, "I've got to give him credit for taking care of the inflation problem, even though he's hurt some of the poor people with those programs he's cut."

Bjork said she worries about her children. A son had to move to Texas to find work. A grown daughter is still living at home because "she can't find a job here that pays more than $4 an hour." It seems "wrong" to her that "they are going to have to pay off the deficit we're running up." She agrees with Mondale that "there is no other way . . . but raising taxes" to stop the flow of red ink.

But when she is asked about Mondale, she said, "He looks so blah. I don't care for him at all. He takes the lowest, puniest potshots at Reagan. I really don't care for him. But I'll try to listen to what he says. I'm just glad I've got two months to make up my mind."