In this staunchly Democratic blue-collar suburb of Pittsburgh just before Tuesday's Pennsylvania presidential primary, voters were so soured by the Carter-Kennedy choice that they were reaching for a third force: saying they are undecided, voting "no preference," even marking the ballot for Jerry Brown.

Out of 64 registered Democratic voters in Oakdale's Election District 2 that we interviewed last Thursday, helped by Patrick Caddell's Cambridge Survey Research, eight told us they would vote for Gov. Edmund G. Brown Jr., who withdrew a month ago but remains on the ballot here. Five other voters volunteered they would check the "no preference" box, new to Pennsylvania. Four others claimed to be still undecided.

Thus, in what was selected for us by Caddell's organization as a statewide barometer of Democratic voting, better than one out of four voters interviewed dodged the Carter-Kennedy choice. These lower-middle income voters (median family income: $15,018) are beaten down by inflation, frightened by rising unemployment and disenchanted with President Carter's efforts to free the Iranian hostages. But they simply do not trust Sen. Edward Kennedy.

The 47 voters willing to choose between the two candidates divided 31 for Carter, 16 for Kennedy. If Election District 2 votes that way Tuesday, it almost certainly will lose the barometric qualities it displayed in 1976 and other recent Democratic primaries; late statewide surveys showed a near dead heat.

Actually, our interviews showed a closer race than 2-to-1 for Carter. Kennedy's voters were more positive than Carter's, and some third-force voters sounded as though they might end up with Kennedy. In any event, voters here do reflect the statewide Democratic impulse of Jimmy no, Teddy no. Both candidates are unpopular and getting more so each day.

That leads a produce clerk's young wife to say she's voting for non-candidate Jerry Brown "because I think he's the least of all evils." The more likely reason is non-familiarity, as expressed by a 28-year-old steelworker backing Brown: "I'm for him because I haven't heard anything about him." Such professed Brown voters may be attracted instead by the "no preference" box when they discover it on the ballot.

Carter's support here is thin to the point of evaporation, typified by the 55-year-old wife of a mine supervisor who called him "not great, but he's honest." The voters interviewed split evenly on approval or disapproval of Carter's Iran policy, but the critics were more vehement.

More important, inflation outpaces Iran, 2-to-1, as the campaign's top issue among these voters, with one in three now saying unemployment is even more important than inflation. Unable to make ends meet amidst raging inflation, voters of Election District 2 see disaster around the corner in a recession.

One soft Carter voter is a 52-year-old State Highway Department worker who backs the president because "he's too dumb to do anything dishonest." He disagrees with Carter's anti-inflation program: "You don't raise the price of gasoline and credit to reduce inflation." He also disapproves of the way Carter has handled the hostage problem and his Olympics boycott.

This unenthusiastic Carter voter favors mandatory wage and price controls, a view shared by an 8-to-1 margin of the voters interviewed. They therefore endorse the main economic tactic advocated by Kennedy, who is seen by these voters as better than Carter at handling unemployment and about the same in fighting inflation. Indeed, Kennedy's rating on foreign policy in general and Iran in particular is only a shade lower than the president's.

Why, then, do only one out of four voters interviewed express support for Kennedy? Chappaquiddick, of course. These voters find Carter more trustworthy than Kennedy by 6-to-1. Only 17 of the 64 voters say they believe the senator's account of Chappaquiddick (and only nine of his 16 avowed supporters).

While Carter's favorable rating among these voters has fallen to 53 percent, Kennedy's is only 36 percent (and Republican Ronald Reagan's is 26 percent). That's the attitude of the 31-year-old wife of a candy factory worker who wants wage-price controls, cannot understand Carter's anti-inflation program and wonders whether Carter's tactics will ever free the hostages. "I don't really think that he [Carter] knows what he's doing, but I don't trust Kennedy," she told us. While losing faith in Carter as a politician, she still respects him as "a good family man and a Christian."

As their television sets picture Carter and Kennedy savaging each other, voters in the borough of Oakdale wonder whether either the president, whose ability they doubt, or his challenger, whose integrity they question, can ease the economic burden oppressing them. While Election District 2 seems useless in forecasting Tuesday's statewide outcome, it mirrors a mood among Pennsylvania's voters best described by a Carteresque noun: malaise.