Montgomery County Council President Rose Crenca and Maryland Del. Peter Franchot have emerged as likely candidates for the Democratic nomination for the congressional seat held by first-term Republican Constance A. Morella, according to leading county Democrats.

Democratic officials had been concerned by the sparse interest in challenging the popular Morella, but they said the current stock market upheaval makes her vulnerable and has energized possible opponents for the 8th District election in November 1988.

State Sen. Ida G. Ruben (D-Silver Spring) and Allan J. Lichtman, an American University history professor, are considering running, while the names of such Democratic stalwarts as Carlton R. Sickles, who served in Congress in the mid-1960s, and former Capitol Hill staff member Leon G. Billings also have been floated.

"What looked like offering up a sacrificial lamb has now turned into an exciting contest . . . with a real shot at the seat," said Stanton J. Gildenhorn, a former county Democratic Party chairman.

The county and national Democratic establishment has targeted Morella for defeat, believing that a victory by her next year would lock her and the Republican Party's hold on the congressional seat. "We don't want another Gude," said Gildenhorn, referring to former Republican representative Gilbert Gude, who held the seat from 1967 to 1977.

The Democratic Congressional Campaign Committee sees the 8th District as very "doable" for the Democrats and will get involved "in every way possible" to assist a Democratic victory, said committee spokesman Howard Schloss. But he said it is too soon to define the extent of that involvement.

Morella, in a tight race last year, defeated Democratic state Sen. Stewart Bainum Jr. to succeed Michael D. Barnes, who, to the chagrin of some of his party members, gave up the seat to run for the U.S. Senate. While the district is 2-to-1 Democratic, Morella generally is viewed as a formidable opponent, with a winning personality that serves her well on the stump and an ambitious program of constituent service in which she spends considerable time at county functions.

"If more than two people meet in Montgomery County, Connie makes it three," Gildenhorn said with some admiration. "She is a professional nice person," said Edmond Rovner, an aide to Democratic County Executive Sidney Kramer.

Morella has honed her image as a moderate Republican who does not necessarily adhere to her party's line but usually votes the liberal-to-moderate social views of her district. "She's Mac Mathias in drag," said one Democrat, referring to former three-term senator Charles McC. Mathias Jr. (R-Md.), whose moderate politics helped set a formula of success for GOP candidates in heavily Democratic Maryland.

The 8th District takes in the cosmopolitan eastern portion of the county and extends past the booming subdivisions of Gaithersburg. It is a diverse 226 square miles from the multicultural neighborhoods of Takoma Park to the rural fields of Brookeville to the palatial homes of Potomac. Its 318,044 registered voters are some of the most affluent and best educated in the country, about 20 percent of them federal employes.

Much of the early debate in Montgomery political circles had centered on just how winnable the seat is and how much to commit to the effort. Gilbert B. Lessenco, a longtime Democratic activist who had been considering entering the race, said he took himself out, in part because he did not think that the party wanted to get the seat back seriously enough.

Lessenco emphasized, though, that the political landscape has changed since Oct. 19 when the deepest stock market fall in U.S. history called into question the economic policies of a Republican administration. Schloss said Black Monday kindled interest in congressional races across the nation, including the 8th District. "The economy will be a significant issue of every congressional race," he said.

Lanny J. Davis, Maryland's member on the Democratic National Committee, who twice ran for Congress in the 8th District in the mid-1970s, disagreed that the economy will be a significant factor. "Montgomery County voters like to vote for a good Republican if they can find one," said Davis, noting that the national Democratic sweeps that followed Watergate and Jimmy Carter's election had no effect in the 8th District.

Davis said he is convinced, though, that given the right candidate, Morella is beatable. "The only thing that makes it unwinnable is the self-fulfilling prophecy of making it unwinnable," he said.

With about two months before the Dec. 28 filing deadline for the March primary, potential candidates are making the rounds of the county's political elders as they make their individual assessments of what they need to mount a campaign.

Del. Franchot, a freshman state legislator from Takoma Park who raised $60,000 last year in his upset victory for the District 20 delegate seat, is a former staff director for Rep. Edward Markey (D-Mass.). He has told several Democratic leaders that he definitely will seek the nomination. Franchot said he is leaning toward a run but will not formally announce his decision until Dec. 5.

Crenca, a popular three-term County Council member, is keeping her cards closer to the chest. She has said she is very interested in running but is concerned about the campaign funds she would need to raise and about the impact on her family.

Some veteran political activists are giving Crenca an edge, citing her countywide name recognition, good political instincts and flair for campaigning. Lessenco, saying he will be in her corner if she decides to run, described her as a "feisty populist" who would be a perfect foil to Morella.

Crenca's wavering on her candidacy has given pause to some Democrats who wonder if she has what has been called sufficient "fire in the belly" for the seat. Franchot, with his background on the Hill and recent fund-raising work for the Democratic National Party, is rated as better on the issues and on raising the estimated $500,000 a congressional race will entail.

Sickles and Billings, because of their previous and visible work on Capitol Hill, are considered the best name candidates, but each, while intrigued with running, called himself a longshot at this point.

Billings, who made an unsuccessful bid for the seat last year, has been publicly criticizing Morella. "She is not a moderate Republican, she is a Republican Republican," Billings said. He, Franchot and Lichtman, a political unknown who has impressed county officials with his academic credentials, have identified defense spending, the budget deficit and labor concerns as likely key issues.

Morella said she plans to run on her record: "My record is wide open . . . and it will show I am responsive to my constituency. I go the limit."

As to the economy, Morella said she does not think that it is something to blame on the Republicans but instead requires a bipartisan solution. And, as to the local ramifications, Morella said, "With unemployment in Montgomery County at 2.4 percent . . . and the county debating how many jobs to allow into Silver Spring . . . I think Montgomery County is doing okay for now."