Betty Ann Krahnke, the veteran Montgomery County Council member who has been battling Lou Gehrig's disease for the past 18 months, will announce next week that she is stepping down after nine years in office, sources said yesterday.

Krahnke, 57, a Republican from Chevy Chase who has been suffering from the fatal, paralyzing illness since the spring of 1998, has shared her struggle publicly to further awareness of the incurable malady, formally called amyotrophic lateral sclerosis (ALS).

The disease takes its nickname from the New York Yankees slugger whom it claimed six decades ago.

Krahnke's office said she had a news conference scheduled for Tuesday to discuss her term. Her staff declined to elaborate. Sources said she has decided to resign, a move reported by the Montgomery Gazette yesterday. She has just completed the first year of her third four-year term.

Krahnke announced on a rainy morning in August 1998 outside her home that she had the illness, and reaffirmed her intention to run for reelection that fall.

Over the months, though, the disease, which gradually destroys the motor neurons that carry the brain's messages throughout the body, has increasingly debilitated her.

She suffered several serious falls during her 1998 political campaign, then took to using a motorized scooter and an electric wheelchair in the County Council building in Rockville.

Her speech eventually became so slurred that she began using a computerized synthesizer to speak at council and public meetings. She continued, however, to go to work every day, assisted by a private nurse, her husband and her staff.

And while the illness generally runs its course in three to five years, she had publicly vowed to serve out her term.

Lately, though, the illness has tightened its grip even further. Krahnke had lost the ability to hold her head up and to feed herself, and on Thursday she underwent an outpatient procedure at Suburban Hospital, in which a feeding tube was implanted into her stomach.

Experts say that step is normally taken before an ALS patient's respiration declines to the point that such surgery becomes risky, and usually before the tube is necessary.

The disease eventually makes swallowing dangerous--raising the hazard of choking or inhaling food--and a feeding tube becomes a necessity.

Krahnke's husband, Wilson, who declined to comment on the nature of Tuesday's announcement, said his wife was home resting yesterday and was not feeling well.

He said she does not yet need the feeding tube. "She can still eat," he said. "It's very slow. But she's not had any problems with aspiration, which is getting food down into your lungs."