"I'm neither giving up nor giving in," the 78-year-old actor said in a taped statement played at a news conference at the Beverly Hills Hotel. Heston recorded the message Wednesday.
"My dear friends, colleagues and fans, my physicians have recently told me I may have a neurological disorder whose symptoms are consistent with Alzheimer's disease," he said.
"I wanted to prepare a few words for you now because when the time comes I may not be able to."
Heston, who won a best-actor Oscar for 1959's "Ben-Hur," has appeared in dozens of films over six decades, including "The Ten Commandments," "El Cid" and "Planet of the Apes."
"I worked my whole life on the stage and screen before you," he said. "I found purpose and meaning in your response. For an actor, there is no greater loss than the loss of his audience. I can part the Red Sea, but I can't part with you."
Heston's most prominent role since 1998 has been as president of the National Rifle Association. He's asked to finish out his term, which ends in April, said NRA chief executive officer Wayne LaPierre.
His recorded statement Friday was reminiscent of Ronald Reagan's "sunset of my life" letter, in which he revealed he had been diagnosed with Alzheimer's.
"I applaud his going public with the information," Nancy Reagan said in a written statement Friday. "Our family knows all too well the cruelty of this disease and we pray that God will give the Heston family, especially (his wife) Lydia ... the strength to face each day that lies ahead."
Some 4 million Americans have the neurological disorder, which destroys brain cells and causes memory loss. Alzheimer's patients eventually need 24-hour care and usually live eight to 10 years after diagnosis.
Earlier this week, family members of Pauline Phillips, creator of the Dear Abby advice column, said she's suffering from the disease.
Heston was slow and deliberate as he spoke before a blue drape background.
"For now, I'm not changing anything," he said. "I'll insist on work when I can. The doctors will insist on rest when I must."
"If you see a little less spring in my step, if your name fails to leap to my lips, you'll know why. And if I tell you a funny story for the second time, please, laugh anyway."
Heston said he's "still the fighter that Dr. King and JFK and Ronald Reagan knew."
As well known for his political activism as his acting, he also made some predictions for the country.
"I'm confident about the future of America. I believe in you. I know that the future of our country, our culture and our children is in good hands," Heston said. "I know you will continue to meet adversity with strength and resilience as our ancestors did and come through with flying colors — the ones on Old Glory."
Born Charles Carter in a Chicago suburb, Heston grew up mostly in Michigan. Calling himself Charlton Heston from his mother's maiden name and his stepfather's last name, he won an acting scholarship to Northwestern University in 1941.
In 1943, he enlisted in the Army Air Force and served as a radio-gunner in the Aleutian Islands. A year later, he married another Northwestern drama student, Lydia Clarke.
After his army discharge in 1947, the couple moved to New York to seek acting jobs. Heston earned star billing in his first Hollywood movie, "Dark City," a 1950 film noir. Cecil B. DeMille cast him next as the circus manager in the all-star 1952 film "The Greatest Show On Earth," which won the Academy Award for best picture.
"I am grateful for the gift of the greatest words ever written to let me share with you the infinite scope of the human experience," he said Friday. "As an actor, I'm thankful that I've lived not one life, but many."