In a matter of hours on Christmas Eve, Maryland Del. Peter Franchot went from front-runner to underdog in the race to become the Democratic candidate for Congress in the state's 8th District.

Michael L. Gudis, a veteran Montgomery County Council member, entered the field. Not only did he get the immediate and important backing of County Executive Sidney Kramer and a host of other party activists, but Gudis also picked up state Sen. Laurence Levitan's endorsement. Levitan just last month had stood amid the balloons and placards of Franchot's fledgling campaign and endorsed the freshman Takoma Park legislator.

"Larry Levitan is an old friend of Mike Gudis, and that is understandable," Franchot said, with the most calm he could muster at Levitan's abrupt reversal.

Levitan's change of heart is an indicator of how the Democratic congressional campaign is shaping up as a contest of political old-timers versus a newcomer. It is an important race for the Montgomery Democrats, who fear that first-term Republican Rep. Constance A. Morella could become an entrenched power if she wins again. This fear is now compounded by the prospect that their best chance of defeating Morella may become buried in a political cross fire between Franchot and Gudis.

Interviews last week with Democratic activists and officeholders in Montgomery -- including backers of Franchot and Gudis and those staying neutral -- showed that the embracing of Gudis by key members of the county political establishment stems more from the unease they have with Franchot than from real enthusiasm for Gudis' candidacy.

Franchot, 40, is a newcomer to Montgomery County and its politics. He has served in the General Assembly for just a year, winning the District 20 seat through an independent campaign of direct mail and aggressive door knocking that upset three candidates endorsed by the countywide Democratic incumbents' slate.

"He's an unknown, an outsider. He's got a fresh face and fresh ideas and he's a threat. And, because of that and because he hasn't 'paid his dues,' he has to be put in his place," said one officeholder who supports Franchot. "No matter that Franchot is attractive, articulate, intelligent and knows and cares about the issues."

Gudis, on the other hand, is a known and established quantity. At 51, he is serving his third term on the council, experience that his supporters say makes him better on the issues that matter to the county and that gives him the contacts and name recognition to be the party's standard bearer against Morella.

Those contacts have already paid off in the backing of Kramer and an influential network of Democratic activists who surround him. "I have known Gudis for 15 years. I feel more comfortable with him, as opposed to a relative newcomer who has made an effort to be a loner and is generally unknown even to his colleagues," said Stanton J. Gildenhorn, a former county Democratic Party chairman.

Franchot bristles at such talk, saying "I am an outsider the same way {former Rep. Michael} Mike Barnes was an outsider . . . an independent voice in Congress."

While Franchot, a former congressional staff director, concedes that the events of the last two weeks make him an underdog, he is still regarded as an impressive campaigner. Franchot's 1986 legislative race, some Democrats said, was probably more of a test than Gudis' runs for county council. While Gudis had the advantage of running and winning countywide, he did so only as part of a Democratic Party slate.

And, there are liabilities in the Gudis candidacy. Perhaps foremost is the perception among County Council observers that he is weak and indecisive. His public hesitation on how to vote on the controversial appointment of John P. Hewitt to the Planning Board gave rise to months of jokes about him, some of which made it into local newspapers.

Gudis acknowledged that some people perceive him as someone who sits on the fence. But he said it is a result of his style of waiting until all the facts are in before making a decision.

Gudis' vote in support of Hewitt, who had been accused of failing to combat racial discrimination while he was a county official, aroused the ire of the county NAACP, which in recent months picketed Gudis' house. His hiring of his girlfriend and campaign manager, Patricia Clark, as his administrative aide, albeit legal, caused Gudis some political embarrassment.

"Any elected official has a certain amount of baggage. Franchot has his. Gudis has his. It can't be denied. But, then, I cannot think of a perfect candidate the party could run with no liability," Gildenhorn said.

County Democrats are uncertain what effect the intraparty rivalry will have on their chance of beating Morella next November. Morella is an engaging officeholder, popular with most constituents and well-liked by politicians of both parties. But she is an aberration in a county where Democrats dominate by sheer numbers and at all levels of government. Her victory in a tight 1986 race against state Sen. Stewart Bainum Jr. embarrassed Democrats who enjoy a 2-to-1 edge in party enrollment.

The district, spanning the southern and eastern parts of the county from the D.C. border to Gaithersburg, has had its share of Republican congressmen. But Democrats, who held the seat from 1979 to 1986 under Michael D. Barnes, tend to view it as their property. This was to be the year, Democratic activists proclaimed, to get back the seat.

But for much of 1987, no prominent Democrats could be enlisted to step forward. Barnes, who gave up the seat in his unsuccessful bid for the U.S. Senate, said he wasn't interested.

Neither was County Council member Rose Crenca, state Del. Nancy Kopp, nor Blair Lee, scion of Montgomery's first family of politics.

"It's a good question," longtime party activist Edmond Rovner said of why a likely candidate or candidates didn't emerge sooner. Rovner, an aide to Kramer, suspects that the bloody and crowded 1986 primary may be a factor. In 1986, Bainum won after a bitter primary over former representative Carlton Sickles, County Council member Esther Gelman and former Capitol Hill staffer Leon G. Billings. "Such good people canceled each other out last time . . . maybe that scared a lot of good people off this time," Rovner said.

There are also some who think that despite their public statements, Democratic officeholders have a vested interest in not wanting a Democrat in Congress. "A Democratic congressman like Mike Barnes diminishes the influence and power of local leaders," said one activist.

Beating Morella, most Democrats agree, has become harder with Gudis and Franchot and their respective supporters in the party going at one another. Five other lesser-known Democrats have also filed for the March 8 primary, although one, American University Prof. Allan J. Lichtman, said he is assessing whether to withdraw from the race.

"What concerns me is that when we won the seat it was when we were united and together behind one candidate," said Gilbert Lessenco, a Democratic activist who had considered running for Congress himself.

Lessenco and others think there is still a chance that if the primary sticks to the issues, serving as a way of focusing attention on the Democrats, there is still time for the party to unite behind one candidate.

That hasn't always happened in the past, but this year the primary is earlier, allowing an unprecedented eight months for the party factions to heal their wounds.

"We have a bloody tradition of eating our own," Crenca said. "We'll see if we can put it to rest."