Apprehension shadowed Walter Mondale last week as he retailed his politics a third straight day in Maine, seeking support for a straw vote that should be a minor way station in the Democratic presidential marathon.

It is anything but minor for Mondale. The state Democratic convention here Oct. 1, at which delegates will cast presidential preference ballots meaningless in terms of the actual nominating process, has become crucial to him. A defeat by party regulars, his bedrock strength, would be devastating. Indeed, anything less than impressive victory would hurt.

That's why Mondalites are apprehensive about Maine, a microcosm of his uneasy front-runner status nationally. Most of the 3,000 state convention delegates (of whom about half are apt to show up in Augusta Oct. 1) say they are undecided. Beyond reflecting the Down East personality, these Democratic Party workers also are flashing this message: Mondale has not turned them on, and they harbor doubts about his electability.

Accordingly, Democratic insiders here doubt an overwhelming Mondale win and even suggest the remote possibility he might finish second. John Glenn's political managers decided not to make a major effort for the straw vote. That renders Maine even more politically surrealistic. Mondale's principal challenger here seems to be the other Fritz: Sen. Ernest Hollings of South Carolina.

Key 1980 Carter-Mondale leaders here who trashed Ted Kennedy's challenge in his back yard are supporting Hollings. Maine Democrats attribute that to a high-and-mighty attitude earlier this year by the Mondale campaign that ignored its faithful.

But Hollings has more than big names. The handsome, courtly southerner has charmed Maine by concentrating his campaign in this thinly populated state. Although the Maine Teachers Association is likely to follow the National Education Association's preference for Mondale, teachers who had just heard him speak in Portland told us their hearts are with Hollings.

Earlier that day in Augusta, one liberal delegate confided a preference for Hollings "because he's a real southern gentleman." That reason may reflect belief that the straw vote really settles nothing, permitting a free vote.

Compounding Mondale's problems here is his nemesis on the left: Sen. Alan Cranston. Cranston has virtually transplanted his national staff in the soil of Maine, which is not at all rocky for nuclear freeze advocates. Meeting such delegates (who seem largely unaffected by the Korean airliner incident), Mondale declares a bit plaintively: "I was the first candidate to call for such a freeze."

Realizing that nothing less than victory is acceptable here, the well-oiled Mondale operation has applied the pressure on this small state. The budget is estimated at a staggering $200,000 to $250,000. More than 50 bright young Mondale organizers blanket the state.

Mondale himself has scheduled seven days here in the month of September, showering attention on individual voters that would seem excessive even for a city council race. In understated Maine, Mondale's high-powered stump style was traded in for a conversational tone seldom interrupted by applause.

His remarks at delegate receptions concentrate on reciting the full panoply of President Reagan's alleged sins. Although Mondale's inclusion of nerve gas along with the B1 and MX as unacceptable "major" weapons systems seems directed against Glenn, he specifically mentions no Democratic presidential rival. Mondale talks about the KAL 007 disaster only when asked, then suggests sanctions that "sting more" than Reagan's-- such as higher interest rates on East Bloc loans. But he rules out a grain embargo or interrupted arms control talks.

Mondale's performance is amiable and error-free, and he displays seemingly inexhaustible good will engaging in mind-numbing small talk. But his intent listeners give no sign that they feel themselves in the presence of the next president.

Therein lies the problem of the uneasy front-runner. He can hardly afford a close call, much less an upset loss in Maine on the eve of certain endorsement by the NEA and AFL-CIO. But whatever the outcome, the fact he had to sweat it out here in a field that does not include John Glenn reveals doubts among even friendly Democrats over whether he is really the Democrat to beat Ronald Reagan. Copyright (c) 1983, Field Enterprises, Inc..