After weeks of doggedly pursuing Democratic Rep. Michael D. Barnes through some of the most liberal pockets of Montgomery County, Albert Ceccone, Barnes' Republican rival in next Tuesday's election, recently found in Bethesda what should have been the perfect audience for Ceccone's unabashedly conservative views.

Standing before 100 retired military officers one night, Ceccone blasted Barnes' voting record on defense and foreign policy issues and then pronounced the three-term Congressman to be "so far left he's left Montgomery County."

But at those words, the once-polite audience turned hostile. One woman in the crowd cried "No!" and dozens of others loudly jeered Ceccone's statement. Ceccone, an able stump speaker, was left speechless; Barnes, seated near him, never altered his deadpan expression.

Therein lies Al Ceccone's worst difficulty in what has shaped up as one of Maryland's most lopsided congressional races: Barnes' popularity in the 8th district has never been higher, even as the district has turned somewhat conservative and may be won by President Reagan next week, just as it was in 1980.

Stretching from wealthy Jewish enclaves of Bethesda, through working-class neighborhoods of Wheaton and Rockville and north to the rows of Yuppie-owned town houses in Montgomery Village, the 8th is at once a politician's dream and nightmare. A community meeting in Silver Spring may be a convenient 30-minute drive from Capitol Hill, but the congressman is apt to find a federal worker there eager to dissect his latest vote on government employe pensions.

Since his first election in 1978 when he unseated popular Republican Newton I. Steers, Barnes, 40, has cultivated those highly educated constituents through strong local services and thoughtful, generally moderate stands on issues affecting his district of 580,000 residents.

As chairman of the House Foreign Affairs subcommittee on Western Hemisphere affairs, Barnes has emerged as one of his party's spokesmen on Central America and has achieved the kind of national visibility that Montgomery County voters have come to expect of their elected representatives.

His campaign treasury bulging with at least 10 times the $12,500 raised by Ceccone, the incumbent is coasting comfortably to an expected fourth term. Indeed, late last month, after a series of debates with Ceccone, Barnes was confident enough to say, "The campaign hasn't started yet."

Yesterday, Brian E. Barkley, a Rockville lawyer and Barnes' campaign manager, said his candidate may repeat his 1982 performance and capture 71 percent of the vote, a record for the district.

"There's no such thing as a piece-of-cake campaign but . . . a win is there," Barkley said.

In addition to Ceccone, Barnes also faces Libertarian candidate Samuel K. Grove, a 33-year-old electronics technician from Gaithersburg who observers believe has a minuscule chance of winning.

Ceccone (pronounced Che-cone-ee), a Chevy Chase real estate and investment counselor, believes his conservative views and proclaimed alliance with Reagan administration policies have broad appeal in Montgomery, though registered Democrats there enjoy a 2-to-1 advantage over Republicans.

"I don't agree with the assessment that the county is all-liberal," Ceccone, 38, said in a recent interview. "I will defintely get some of Reagan's coattails and some anti-incumbent feeling.

"And I may win," he added.

Ceccone, twice an unsuccessful candidate for countywide office, says he has an advantage by posing a stark alternative to Barnes, who in the past has faced relatively liberal Republicans.

While Barnes has supported some federal funding for abortions, Ceccone opposes abortion. Barnes repeatedly has urged that U.S. aid to Central American governments be contigent on their human rights programs; Ceccone repeatedly warns of a persistent "Communist threat" to those regimes.

Ceccone also has criticized Barnes as a "tool" of Speaker Thomas P. O'Neill and for "shooting from the hip and attacking" President Reagan's decision to invade Grenada last year. Ironically, Barnes says the harshest criticism he has ever received from Montgomery County liberals was their blistering mail against his belated endorsement of the invasion.

"Al has been working very hard, doing all the things a candidate has to do," said Allan C. Levey, a Potomac resident and head of Maryland's Republican Party. But "he's running against a very popular candidate and one of his problems . . . is that his race was not targeted," a reference to help from national and congressional GOP strategists.

Indeed, some top Republican officials say Barnes' popularity was the key factor in the party leadership's decision to spurn Ceccone.

Also cramping Ceccone's campaign have been his occasional gaffes and speaking style, which is far less smooth than Barnes'.

Their encounter last month before 100 members of the Retired Officers Association was typical.

Playing to his audience at the officers club at Bethesda Naval Hospital, Barnes joked twice about his former lowly status as a Marine Corps corporal and took pains to mention his endorsement by a Veterans of Foreign Wars group.

Ceccone, on the other hand, incorrectly identified the Pentagon's highly publicized Stealth bomber proposal as "the Stealth missile."

After Barnes pointed out the mistake, Ceccone said: "I'll admit I don't know the difference between a Stealth missile or bomber . . . . But we should stay the course with President Reagan."

Many Montgomery residents, including some Democrats, believe that a well-financed and moderate-to-liberal Republican could one day pose a serious political threat to Barnes. Keith Haller, a political pollster from Rockville who managed Barnes' first campaign, said the rapidly changing county "is open to new leadership."

But Barnes "has developed respect and popularity and that just doesn't happen overnight," Haller said. "He has melded nicely with the county. That leaves him in a very good position this year.