It is early evening here, and the lights stream onto the green turf of the Olympic stadium. In the center is a stage, and the backdrop is a bright blue curtain with a Canadian maple leaf and the number "50" in the middle. About 40 men and women, carrying the flags of countries from all over the world, march forward.

This ceremony yesterday marked the formal opening of an international convention for Alcoholics Anonymous on the occasion of AA's 50th anniversary. There is a tremendous sense of having survived a disaster together, a friendliness that has nothing to do with the woozy jocularity of so many conventions.

"My God," said a woman yesterday, referring to those already registered. "Can you believe that there are 45,000 former drunks walking around here sober?"

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"Nobody thought this thing would last. Nobody envisioned the way it would spread," said Ed M., an AA spokesman here.

The growth of AA is a worldwide phenomenon. Younger people are joining, with a 20 percent growth in the under-30 group. Women now make up over a third of the membership. With well over 655,000 members in the United States and Canada, there are at least another 468,834 AA members scattered throughout the rest of the world.

As you would expect, there are stories. Lee A., an attractive woman who got sober 30 years ago, told a group, "I started out as a very dainty, ladylike woman, overly brought up, I like to say, and very much the lady. I ended up on a barstool on Third Avenue in New York."

Pat P. told the audience, "I knew that something was terribly wrong with me, but it never occurred to me that it was alcohol. Alcohol was my friend, it was the only thing that helped me, I thought. My father was an alcoholic and I hated what I'd seen alcohol do to our family. That would never happen to me." But it happened.

Above all, though, you get a sense here of sheer numbers. AA is even cracking the Iron Curtain, with at least 48 groups established in Poland since 1981.

Fifty-four countries are represented in Montreal for events that began Thursday and conclude tomorrow. You see people from Sri Lanka, India, Korea, Turkey and Japan. And from Finland, Italy, Germany and Israel. Since AA is an anonymous fellowship with no dues or fees, no formal records are kept of members. So estimates of membership are generally conservative.

Among those here are at least 12,000 members of Alanon. Established in 1951 for the friends and families of alcoholics by Lois Wilson, wife of AA cofounder Bill Wilson, Alanon has grown so rapidly that for the first time it is holding its own international conference simultaneously.

At 94, Lois Wilson is still speaking to a sold-out crowd. Within Alanon has grown Alateen, for teen-age children and siblings of alcoholics, as well as the latest movement, Adult Children of Alcoholics. Only 4 years old, there are approximately 700 Alanon groups focusing on the issues of adult children of alcoholics, recognizing that alcoholism infects every member of a family.

AA cofounders Bill Wilson and Dr. Bob Smith are dead, but "Dr. Bob" is survived by his son, Bob S., who was here to speak to Alanon. Late Thursday afternoon, Bob S. recalled much of the lore of AA: the meeting in Akron, Ohio, 50 years ago between Dr. Bob and Wilson; their contacts with Henrietta Sieberling, a member of the Oxford Group, an early friend of AA; the formulation of the first AA principles; the publication in 1939 of "Alcoholics Anonymous," commonly referred to as the "Big Book," a compilation by Wilson of the experiences of the first 100 AA members on getting and maintaining sobriety.

"Between the time he met Bill Wilson and sobered up and the time he died," Bob S. said of his father, "he treated over 5,000 alcoholics free of charge. What he and Bill figured out was the key was working with others, one drunk talking to another, sharing their experience, strength and hope. Dad and Bill started bringing drunks home right away to work with after they met, moved right into our house as well. One old-timer stayed with us for over a year. There was an immediate change in Dad after he met Bill. Mother and I and my sister could see it right away."

For a moment yesterday, AA members stood as their country of origin was called out. AA crossed all lines, all divisions of race, religion, nationality. They held hands for the traditional closing.