Montgomery County Council member David Lee Scull ended months of speculation yesterday by announcing that he will not challenge the reelection bid of County Executive Charles W. Gilchrist in this year's Democratic primary.

Scull's announcement may assure that Gilchrist will not face strong primary opposition, eliminating the possibility of a bitter campaign that would have benefitted the county's Republican party.

Scull, who called the decision the toughest of his life, had been under pressure to avoid a divisive challenge. But several politicians indicated yesterday they were shocked by his announcement.

"I'm dumbfounded," said Democratic State Sen. Victor Crawford, who had approached Scull as recently as Wednesday to indicate that there was strong sentiment among Democrats in the county's delegation to the state legislature "to avoid a confrontation at the highest levels of county politics . . . I had every indication that he was going to run."

Scull's decision to seek reelection to the County Council instead of running for executive could set up a general election contest pitting Gilchrist against Republican State Del. Luiz Simmons in November. Simmons has been called the strongest potential candidate by the county's Republican chairman, Paul Clark, who adds that Simmons probably could win his party's nomination without challenge.

Gilchrist said that as a result of Scull's announcement "the potential level of bitterness that could have appeared will now disappear" and that he was pleased he would not have to face a tough primary fight.

The executive appears to have backing from both the majority of the county's Democratic state legislators and the local Democratic party organization.

Scull, 39, a former state delegate and chairman of the county's delegation, has political assets that include name recognition, substantial financial resources and a family history of prominent involvement in local politics.

Scull's father, David, and mother, Elizabeth, were presidents of the County Council and his uncle, Blair Lee III, was acting governor of Maryland.

Scull said his candidacy could cause the Democratic party to "emerge from the September primary too divided to be successful in the November general election." He added that an editorial in yesterday's editions of The Washington Post was a factor in his decision. The editorial said that despite "allegations, insinuations, predictions and political whispers of corruption" in Gilchrist's administration over the handling of the county liquor department, the controversy "is neither a useful nor fair issue" in the executive's campaign.

Rockville businessman Wade Ellis Dunn, a political unknown, is the only formally announced Democratic candidate for county executive. He said yesterday he believes his chances for winning are strong.

Scull, who pledged yesterday to support each Democratic nominee, twice has made critical statements about the Gilchrist adminstration. On Feb. 12 he called on Gilchrist to "cleanse his administration of the stain created" by the liquor controversy and called on the executive to fire officials who violate county personnel regulations.

Yesterday Scull continued to speak out, saying he has been "very disappointed by the administration's performance" in the liquor department controversy. "Although the actions involved may not have violated any criminal statute, they were well below the standards expected of public officials in this county," he said.