They called her a good friend and an honorable politician, and as they filled the small hearing room in Rockville with tears and applause yesterday, they bade their failing colleague Godspeed.

Montgomery County Council member Betty Ann Krahnke, who has been battling Lou Gehrig's disease for 18 months, announced yesterday that she will step down from the County Council, effective April 17, after nine years in office.

A Republican from Chevy Chase, Krahnke said she would work through the council's annual spring budget deliberations and step down after the March primary and a special election to fill her seat. The date for the special election, mandated by legislation passed last spring, will probably be set by the council next week. Officials said it will be the first such election in the council's history. Previous vacancies were filled by appointments.

Krahnke, 57, made the announcement at 1 p.m. before a large, tearful crowd of council officials, staff members, friends and relatives who packed the seventh-floor hearing room of the council's office building in Rockville.

She received a standing ovation after entering the chamber in a motorized wheelchair and delivering a moving speech via computerized voice synthesizer.

"Today is a bittersweet day for me," she said. "In several months, when I close the door to my council office for the last time, I will feel great pride knowing my footprints will linger, yet the pull of unfinished business, projects left undone will be strong."

"Nearly a year and a half ago, when I stood on the front lawn of my house and vowed to fight Lou Gehrig's disease and continue to serve, I had high hopes for finishing out my four-year term," she said, as she sat behind the hearing table flanked by her husband, Wilson, and two of their three daughters, Carolyn Schugar and Peggy Enright.

"Unfortunately, not even top medical experts were able to predict how quickly this terrible disease would progress," she said. "At that time, I pledged I would reassess my ability to serve when it became necessary to do so. That time has come.

"Shortly after Christmas, with guidance from my family, I decided my illness had progressed to the point where in a few months, carrying out my duties will become extremely difficult."

Krahnke, the daughter of an FBI agent, announced in August of 1998 that she was suffering from Lou Gehrig's disease, the fatal, gradually paralyzing illness formally known as amyotrophic lateral sclerosis.

She vowed, though, to seek reelection, which she did successfully that fall, and then to serve out her term. She held her post effectively, with the help of her staff, family and electronic aids.

But over time, the illness robbed her of the ability to walk, talk, write and feed herself. Last week, she had a feeding tube implanted in her stomach.

Yesterday, clad in a purple suit and blue and red print blouse, she smiled and nodded to fellow council members and friends.

"I am deeply saddened that I will be absent in coming years and unable to see certain projects dear to my heart through to fruition," she said.

Council President Michael L. Subin (D-At Large), then took the floor. He said he had worked with Krahnke for almost 10 years, "but I did not know--nor could any of us have known--the full measure of this remarkable woman until the last year and a half."

"Betty Ann could have wrestled with this illness in private," he said. "Rather than do that, she took on the much more difficult path of a public battle."

"Betty Ann, we love you," he said, "and we'll miss you.

"Godspeed."

CAPTION: "With guidance from my family, I decided my illness had progressed to the point where in a few months, carrying out my duties will become extremely difficult," says Betty Ann Krahnke.