As candidates scrambled for last-minute attention in the close Democratic primary race for Montgomery County executive, County Council President Elizabeth Scull yesterday endorsed Royce Hanson, one of three contenders for the nomination in Tuesday's elections.

Scull, a popular council member, praised Hanson for his "experience, knowledge" and "judgement" demonstrated during five years as chairman of the county's planning board.

In endorsing Hanson at a press conference, she passed over Hanson's opponents - council member John Menke, her colleague for the past four years and council president in 1976-77, and State Sen. Charles Gilchrist.

Supporters of Menke and Gilchrist downplayed Scull's possible influence, citing other endorsements they have received and the "momentum" in their own campaigns.

Hanson said he was grateful for Scull's public endorsements at this "crucial" point of a hard-fought executive race in which some polls say half the voters are still undecided.

"Betty has a real strong basis of support in this community built on a strong record," Hanson said of Scull. "She also has a long record of concern for 'people-problems.'" Scull is the sister of Acting Gov. Blair Lee III.

Her name will not appear on the primary ballot because she is unopposed for reelection. This prevents her from joining a primary slate carrying Hanson's name.

But Scull said she would "recommended him to others who may have confidence in me, and know I know Royce better than they do."

Scull said she supported Hanson because after working with him for five years, she knows he has not only the experience and knowledge but the judgement and philosophy to deal well with the many issues that come before the county executive, and to make well the many decisions that the county executive must make."

She said that although she had supported Hanson for "many months," she waited to announce it to avoid interfering with council business.

She declined to say whether she supports the council candidates on Hanson's slate - incumbents Esther Gelman and Neal Potter, and Mable Granke and Mike Gudis.

Typically, leaders of numerous groups and individuals have passed the word to their followers about their preferences for county executive, but among the independent-minded Montgomery County electorate, such stamps of approval are never sure vote-getters.

Gilchrist has been endorsed by Montgomery County COPE (the AFLCIO political action committee), the Montgomery Federation of Teachers, the Montgomery County Council of Supporting Services, the professional firefighters, Alliance for Democratic Reform, Police Political Action Committee and the Coalition of Presidents (leaders of civic associations). He shared the Montgomery County Education Association endorsement with Hanson.

Hanson also received an "acceptable" rating, form the Suburban Maryland Home builders political education committee. But the home-builders cited Menke as their first choice on their sample ballot.

Menke has conducted a campaign largely independent of the conventional Democratic Party network and has been less vigorous in his pursuit of endorsements.