Washington — The long, brutal Democratic primary campaign exposed deep doubts within the party that its candidate could defeat President Reagan, plus a persistent longing for some mystery candidate who could.
One of those mentioned as a distant hope was once an obscure country lawyer who says there is now ''no chance'' for a surprise candidate to emerge at the convention next month. Too much time, money, energy, and shoe leather have already gone into the campaign, says Sen. Dale Bumpers of Arkansas.
The man who didn't run admits to twinges of regret, but he also says that even if he had, ''a lot of Democrats'' would still be saying the President was unbeatable, ''and I wouldn't look any better to them than anybody else did.''
Senator Bumpers, the object of presidential and now vice-presidential speculation, began his meteoric political climb only 14 years ago in his tiny west Arkansas hometown of Charleston. There he honed his now-famous speaking skill by arguing before juries and by listening to his father, a hardware dealer , give speeches at local events. He made an early, unsuccessful attempt to become a state representative.
Mostly unknown in his state in 1970, he sprang into the governor's office and then into the US Senate, defeating three Arkansas political giants in the process.
''He was one of the best governors we've ever had,'' says conservative columnist John R. Starr of the Arkansas Democrat, probably the harshest critic of Mr. Bumpers's senatorial performance.
Mr. Starr recalls his first meeting with Bumpers. ''He came strolling down a gravel path at Blanchard Cavern,'' a north Arkansas cave, during the dedication by the National Forest Service. The ''major'' gubernatorial candidates were on hand, surrounded by their entourages. Political newcomer Bumpers was accompanied only by a nephew who served as his aide. ''Nobody took him seriously,'' says Starr.
Bumpers won the race over both Democratic former Gov. Orval E. Faubus and incumbent Republican Winthrop Rockefeller. He later went on to defeat Democrat Sen. J. William Fulbright, the legendary Foreign Relations Committee chairman, and win reelection amid the Republican landslide of 1980.
During his years in Washington, Bumpers has earned respect for his eloquence on the Senate floor (he rarely uses a text for his almost daily intonations) and for his daring voting record, which is far more liberal than his constituency. He was the only Southern senator who opposed a bill in 1982 to restrict the courts' ability to order busing for school desegregation.
Back in Little Rock, Starr's view is that ''He got up to Washington and fell with the Eastern establishment crowd'' and lost touch with his fellow Arkansans. But the columnist nonetheless says Bumpers would have made a good presidential candidate.
''He'd be a better candidate'' than either Walter F. Mondale or Colorado Sen. Gary Hart, the journalist says.
Bumpers quashed talk of emerging as the San Francisco surprise. But relaxing in shirt-sleeves in his senatorial office, he is clearly itching for the campaign stump, or at least for a chance to join the charge on President Reagan's record.
The senator is a little sorry that, after taking a test jog down the campaign trail a year ago, he decided not to run in the presidential marathon. ''From a political standpoint it might have been a mistake,'' he says. ''On hindsight, it looks like it might have been doable.''
He maintains that he has lost no sleep over the decision, based mainly on lack of money. But his lengthy soul-searching over whether to run left questions about his decisiveness. He answers with jokes on himself. He told a Maryland Democratic Party banquet recently that one voter a year ago warned him to hurry up and decide to run, because ''you may peak before you announce.''
On the vice-presidency: ''Let me say first, I don't expect the nomination to be offered me,'' he says. He would be flattered, he adds, ''But that is not to say I would accept it.''
The one role he is not shy about wanting, ever since childhood, is the keynote speaker at the San Francisco convention. ''I think the keynoter really sets the tone for the convention,'' Bumpers says.
Whether or not he opens the Democratic convention, he is already tuning up his oratory for the campaign. ''I think there are those Democrats who have sort of a hopeless attitude about it.''
But Bumpers holds that Reagan is vulnerable, chiefly because, in his view, federal deficits are leading the country to economic disaster. He has delivered that message to partisan Democrats and to the Republican-leaning US Chamber of Commerce, and admits it's not yet a winner. He compares the situation to his failure in the cemetery business. ''You know why?'' he asks. ''Selling cemetery lots to healthy people is a very difficult chore.''
Moreover, Mr. Reagan's campaign message is much more cheerful, he says: ''The President's political forte lies in his ability to make people feel good about themselves, feel good about their country, and tell them that we've turned it around and that everything's going to be fine. He does that magnificently. What I quarrel with is the shamelessness of it.''
Bumpers says he's not trying to be ''Elijah or Jeremiah,'' but prophesying economic calamity is exactly what he is doing. ''I think it's just as certain as the night following the day,'' he says, unless action is taken quickly. ''I'm not absolutely sure that the case can be made before November, but I have to keep trying, because I feel so strongly about it.''
The Arkansan, who disavows ''conventional wisdom,'' which he says is usually wrong, has often chosen to paddle against the current.
''He's kind of gone his own way on the issues,'' says Ernest Dumas, editorial writer and columnist with the Arkansas Gazette, the Little Rock paper that has backed Bumpers. Many voters have never forgiven him for helping to ratify the Panama Canal Treaty, Mr. Dumas says. He angered more by refusing to back bills to take court-ordered busing out and put prayers into the public schools.
Dumas concludes that ''he'll have a tough fight in two years (when his term expires), but he'll also be tough to beat.''
If conservative voters at home are displeased, then neither has Bumpers suited liberal groups. He angered unions by refusing to give them a key vote to stop a filibuster in 1979 of a labor reform bill. He voted against the deadline extension for ratifying the Equal Rights Amendment.
He and his wife, Betty, have been strong advocates of arms control. Mrs. Bumpers has been active in a peace organization that has been the subject of attacks from the far right. But despite backing the nuclear-weapons freeze, the senator favors building modern nerve-gas weapons.
He has even sided with the Reagan administration by voting for the 1981 Reagan budget cuts totaling about $56 billion. ''The President was dead right,'' he says. ''There were a lot of programs that were highly marginal. There was a lot of money being wasted.
''The tragedy is, that was almost exactly the amount that the President recommended for a defense increase the next year,'' he says. And that brings him to his current theme of the federal deficit.
If critics call him a ''born again'' budget balancer, at least he is a fervent convert. ''I think it is really shameful not to tell people that we have serious sacrifices to be made in this country,'' he says.