Jeremy Thorpe, whose dashing campaign five years ago led his Liberal Party to a dazzling election showing, is plodding somberly through this campaign, preoccupied with his trial next week on charges of conspiring to murder a man who claims to have been Thorpe's lover.

No longer the third-party standard bearer barnstorming across the whole of England, Thorpe has campaigned determinedly with his wife for his own parliamentary seat, across North Devon's remote moors and villages, its fishing and beach resorts.

His long, lanky figure is stooped over now, his face is drawn and his speeches are subdued and humorless, beginning always with his preamble:

"There are matters which have to be resolved after his election which it would be improper for me to comment on during the course of the campaign. Suffice it to say that I have asserted my innocence and that I eagerly await the opportunity of establishing that."

Liberal Party leaders tried to stop Thorpe from running because would hurt their efforts to maintain or expand the party's strength in Parliament. But Liberals in Devon wanted him to seek re-election and will loyally support him in large numbers, if the warm response he has received during the campaign is any indication.

Long-time residents receive Thorpe as local royalty and remember the jobs and recognition he brought to North Devon during the years when he was on top. They gave him a 6,000-vote majority in 1974, and that might prove just enough cushion for him to hold his seat.

But thousands of new residents have moved to Devon. Thorpe faces a strong Conservative challenger, businessman Tony Speller from Exeter, the Cathedral City to the south, and an attractive Labor candidate, local teacher Tony Saltern, who could take enough votes away from Thorpe to allow Speller to win.

The Conservatives have targeted Thorpe's constituency, where Tories have long vied with Liberals for the seat, as one they should regain to win Thursday's election nationally.

In February 1974, under Thorpe's leadership, the Liberal Party won nearly 20 percent of the votes nationwide, its best showing since 1929.

Then last year, Thorpe, scion of a financially failed aristocratic family, a former student at Eton and Oxford and son and grandson of members of Parliament, was charged with conspiring to murder former male model Norman Scott. In the pretrial hearing, Scott laid bare a seemy side of Thorpe's bon vivant lifestyle, testifying in explicit detail about their alleged love affair.

Because of Thorpe's present notoriety and vulnerability, the race has also attracted more than its share of fringe candidates-six in all, including candidates of the Ecology Party and the Neo-Nazi National Front, and writer Auberon Waugh and his one-man Dog Lover's Party.

Waugh's half-serious, caustic campaign against Thorpe, conducted largely through pointed innuendo in columns he writes for British magazines, has drawn as much national attention as Thorpe's efforts.

But it is just that kind of interference from outsiders that could help convince the proud voters of insular North Devon to rally behind Thorpe as one of their own. According to the campaign manager for Conservative Speller, "It will be a close-run thing." CAPTION: Picture, Jeremy Thorpe, gesturing, talks with a voter in South Molton as his wife, center, listens. AP