A loosely knit group of dissident Democratic Party activists in Montgomery County--upset by what its members see as the party's drift away from open primaries--is mounting the most vigorous attempt to take control of the party's precinct organization since the reform movement of 1963.

Montgomery's Democratic organization, unlike the small Republican Party, holds May elections for the chairmanship and vice chairmanship of the county's 202 precincts. Challenges for precinct offices--thankless jobs that offer little visibility--are rare.

But this time around, several groups wanting more of a say in party affairs have filed their own candidates for about 120 of those precinct positions--in about 40 cases challenging old-time establishment party workers.

The new activists, like their reform counterparts who similarly took over the Democratic precinct organization in the 1963 elections, recognize the potentially powerful role of precinct officials in selecting candidates and handing out literature election day.

This new coalition seeking to wrest control of the party's apparatus represents all the disparate groups that make up the diverse Democratic Party. Organized labor, believing some labor issues have been ignored, is running a huge bloc of candidates. Blacks are challenging sitting precinct officials in at least four cases and Hispanics are running at least seven candidates.

Also running are several longtime party activists and several "outsiders," including 1982 delegate candidates Dennis Lavallee and Gil Genn, who beat the party establishment in the primary and lost in the general election.

Some groups still express rancor about last year's bitter Democratic primary, when incumbents banded together on a slate. Most precinct officials were their loyal foot soldiers, and these new activists want to make sure that doesn't happen again in 1986.

But even more important, many of these new activists see the party moving away from open primaries and back to the old closed conventions in selecting candidates. Party Chairman Jay Bernstein already has appointed a task force to study the convention idea. The clout of precinct officials would be increased in a convention, and many of these labor, black and hispanic activists want to make sure they are on the inside of any future candidate selection process.

The groups all maintain they are acting out of self-interest, with no "organized" plan to control the party. But this takeover bid is indeed well orchestrated, evolving partly out of a series of meetings and telephone calls between the leaders. They include former central committee member and longtime party dissident Joan Lott and Jerry Keker, who managed last year's United Democrats Council slate.