Front-running Walter F. Mondale wishes to convey the impression that it's all over. The Massachusetts State Democratic Committee, on the contrary, wishes to suggest that it has just begun.

To that end, the committee organized a dinner for all the Democratic presidential candidates last Thursday night. Mondale came, but just barely, speaking, and leaving, uncommonly early.

He was, however, severely punished for what the Boston audience considered cavalier and condescending behavior. By the time the last of his fellow candidates had spoken, the pols had decided that the race in the Bay State is, as a result, "wide open."

Mondale had been scheduled to speak before the $150-a-plate meal was put on the table. But with one thing and another--a late start, a speech by Sen. Edward M. Kennedy (D-Mass.) that was supposed to last two minutes and went more like 15, Mondale was served along with the main course.

"There is not a politician in America who can compete with filet mignon," said state Sen. Chet Atkins, the Democratic state chairman.

Mondale had to speak over a sometimey sound system, a racket of chatter and chomping and clanking forks. He had to yell to be heard, and grew red in the face with the strain of it all. He touched a wide range of topics, as would be the case with an acceptance speech.

The 1,500 diners seemed not to feel that their inattention constituted any breach of hospitality.

If their guest, by his untimely performance and departure, was saying that he had better things to do, it was, in their minds, plainly his problem. To them, an evening where Teddy Kennedy baits those still panting in the race he has foregone is rare sport, and anyone choosing to miss it is to be pitied as much as resented.

Actually, Mondale was hurrying to the airport to catch the last plane back to Washington. He had a breakfast meeting Friday morning.

He has been trying for the past few months, ever since the Kennedy withdrawal, to impart a similar sense of urgency to Massachusetts politicians: telling them the train is leaving the station.

While most of them feel that Mondale will be the nominee, they are reluctant to resign themselves to the inevitable.

For one thing, they are still mourning Kennedy. As the Middlesex County registrar of deeds, John Zamparelli, a madly popular local figure who got more applause than any of the presidential candidates, said flatly, "Around here, we all wish Ted Kennedy were still running for president."

Sen. Alan Cranston (D-Calif.) sat next to Zamparelli and asked him what it would take to get his endorsement.

"I'll do whatever Ted wants," Zamparelli replied.

Beyond the sentimental urge to assure Kennedy of quasi-undying fealty, Massachusetts politicians are in the grip of a mania to matter in the presidential election. They are promoting, at their April 9 issues convention, a straw poll, which some enthusiasts are overselling as "the Iowa caucus a year early."

Long after all the speeches had been made and the plates had been cleared away, the nation's most addicted political buffs hung around, chewing over the evening's fare, exulting, "It's not locked."

Their joy comes from no particular rancor toward Mondale, even though his association with Jimmy Carter is considered more reprehensible here than elsewhere, and he chose The Boston Globe as his confidant in detailing the policy differences with Carter that were not evident during his incumbency.

But there was the perverse pleasure of humbling the exalted and a genuine satisfaction that the others had put their best foot forward for the evening.

Cranston spoke of the possibility of the end of the world in a nuclear attack, amid a deathly hush.

Sen. John Glenn (Ohio) made them laugh with his frontal assault on his reputation as a deadly speaker and twitted Kennedy about the worth of his endorsement of Chicago Mayor Jane Byrne.

Sen. Gary Hart (Colo.) won hearts by coming down among the tables during the long interval after Mondale's departure and making a strong pitch for the nuclear freeze, by far the paramount issue in Massachusetts.

Even Sen. Ernest F. Hollings (S.C.), who some Bostonians frankly said should have brought an interpreter for his deep-fried South Carolina accent, looked good, and they liked him for hanging in.

Sen. Dale Bumpers (Ark.), who has yet to declare, benefitted most from the front-runner's slip. He spoke with genuine passion about the role of government in helping people, as he knew it from his own childhood. Massachusetts activists have been eyeing him. They find Mondale a cautious constituency-collector. They think Bumpers, who can be daring, is their type.

Said state Chairman Atkins, "If you were to have taken a poll that night on just who scored the most points, it would have been Bumpers walking away."