Former President on Alzheimer’s Roller Coaster : Disease: Ronald Reagan is reported to be happy and physically vigorous as he experiences both good days and bad. One day, a friend says, he couldn’t remember having lived in the White House.

Seven months after Ronald Reagan announced he was suffering from Alzheimer’s disease, an incurable neurological disorder that steadily destroys memory, friends and associates of the 84-year-old former President say he is happy and physically vigorous but mentally on a gentle roller coaster of good and bad days.

In April, a distressed Nancy Reagan told a friend that her husband had recently seen the White House on television and, on that particular day, the friend said, Ronald Reagan could not remember ever having lived there.

But a former staff member, Frederick J. Ryan Jr., says that when he saw Reagan in mid-May in Los Angeles, the former chief executive was well aware of his years in Washington. “He had no problem at all recalling his presidency,” Ryan said.

Alzheimer’s specialists, who emphasized they were not in any way commenting on Ronald Reagan’s case in particular, said a pattern of forgetting something one day and remembering it the next is typical of the disorder.

“We’ve come to realize that the chemistry of the brain can change a lot from day to day, even though overall the course of the disease is steadily downhill,” said Marilyn Albert, the director of gerontology research at Massachusetts General Hospital and an associate professor at Harvard Medical School who has studied Alzheimer’s for 18 years.

“Alzheimer’s is a disease, like any other disease--cancer, heart disease, whatever,” Nancy Reagan said in a short speech in New York on June 5. “But unfortunately, for far too long, people have been embarrassed and self-conscious about admitting it. As time goes by, and people live longer lives, this becomes an enormous problem.”

Nancy Reagan closed her remarks at the Hotel Pierre by saying that Alzheimer’s is a “really very cruel disease” and that the families of victims need support and understanding.

“Because, for the caregiver,” she said, as her eyes reddened and her voice broke, “it’s a long goodby.”

In recent months, poignant stories about Ronald Reagan have been circulating among his friends. Six weeks ago, Earle and Marian Jorgenson were the hosts of a dinner for the Reagans at Matteo’s, a popular celebrity restaurant in Westwood. Larry Cullen, the restaurant’s manager, said the room broke into applause as the former President was leaving, which has always happened when the Reagans dined there over the years. But on this night Reagan was not aware that the applause was for him.

Nancy Reagan gently guided him to turn and accept the ovation, at which point Reagan jumped to attention and, with a big smile, saluted the room. His friends were in tears.

Reagan announced in November, 1994, that he was in the early stages of Alzheimer’s, and at the time released a handwritten letter that was applauded for its frankness and courage. “I now begin the journey that will lead me into the sunset of my life,” he wrote. “I know that for America there will always be a bright dawn ahead.”

The average duration of Alzheimer’s disease is seven to 10 years, and it eventually leads to death. There are an estimated 4 million people suffering from Alzheimer’s in the United States, most of them older than 65. Since the announcement, the Reagans have received 50,000 pieces of mail from people in the United States and overseas.

“I want to let other victims and their families know they are not alone in their struggle,” Nancy Reagan said in her speech in New York, where she accepted an award from the Harvard Mahoney Neuroscience Institute. The award recognized the Reagans for helping to increase public awareness of neurodegenerative diseases.

Friends say Ronald Reagan continues to go to his office from 10 a.m. to 3 p.m. every day in Los Angeles, where he meets with visitors, signs books and photographs for supporters and handles paperwork. He exercises every morning with a personal trainer at a Los Angeles gym, plays golf once a week, attends church on Sunday, chops wood at his ranch and goes to small dinner parties with longtime friends. Those who have seen him in the past year say he looks fit and healthy, and that he is not rapidly deteriorating, as sometimes happens with Alzheimer’s patients.

Brian Mulroney, the former prime minister of Canada, a friend of the Reagans and Nancy Reagan’s dinner partner at the awards ceremony in New York, said he last saw the former President 10 months ago. “He was like he always was--vigorous and funny,” Mulroney said. “I noticed things, you know, but my own father died when he was quite young, so I thought this was just a person getting old. It was nothing like, “ ‘Oh my God, Ron is sick.’ It’s just a gentle progression.”

Another family friend says that Reagan seems more dependent than ever on his wife. “When I talk to her now on the phone, he is in the background asking questions every 30 seconds,” the friend said. “What used to be 30-minute conversations with her are now five.”

Other friends say they call Mrs. Reagan to keep her spirits up, but hesitate to badger her with questions. In any case, they say, she does not like to talk about her husband’s disease in much detail.