By an overwhelming majority, members attending the Kiwanis International convention here voted yesterday to allow women to join the 72-year-old community service organization, which becomes the third such group to open its membership to women.

The amendment, approved when an estimated 80 percent of about 8,600 delegates stood in approval at the Washington Convention Center, changes the membership rules to allow individual chapters to abide by respective state laws regarding sex discrimination. Officials said the action was destined to happen.

"I'm happy with the resolution of the issue," said Frank J. DiNoto, president of the club. "I think the ultimate result will be the strengthening of Kiwanis International."

The decision, which affects 315,000 members in 8,200 clubs in 70 countries, follows on the heels of a two-month-old Supreme Court ruling that opened the doors of all-male Rotary service clubs to females.

On Saturday, another major service club, Lions Club International, voted by a 77 percent majority to break its 70-year tradition on barring women.

Yesterday's decision was lauded by Kiwanis officials, who feared mounting legal challenges by local chapters that started admitting women in recent years. An 18-member international board of trustees voted unanimously to recommend the change.

Forty clubs in 16 states have acted on their own to admit women as members in the last 16 months. If the resolution had not passed by a two-thirds majority, the board would have been forced to take legal action against those chapters.

"It's a great deal of relief," said Rex Derr, president of the Olympia, Wash., chapter, which has 14 women members and was a sponsor of the resolution. "Now we can divert that energy we have been spending fighting for change to community service projects."

The resolution, which had been repeatedly struck down, had been gaining popularity in recent years. When the first convention debate on women membership was held in 1973, there was almost no support. By 1977, support for the resolution had grown to 15 percent. But last year in Houston, support grew to 47 percent among convention delegates.

Even with the passage, many delegates warned that individual chapters can still bar women and that the resolution probably would do little to increase the number of females in the organization. Prospective members who have been invited to join the club must be approved by a board of members.

"It really changes very little for a lot of clubs," Derr said. "A club can still reject a woman or a man on the discretion of its members."

DiNoto agreed in a separate interview and said "there will be a modest increase in membership" as a result of the resolution.

Currently there are about 120 women members in the 40 chapters that had been fighting the all-male provision of the organization's charter, a spokesman said.

The stand-up vote came after the passage of an amendment to the amendment that called on other nations to abide by the charter. The original resolution applied only to chapters in the United States.

"This decision sounds the death knell for male-only economic organizations," said Eleanor Smeal, president of National Organization for Women.

Still, one delegate from Kalamazoo, Mich., Ivan Holden, said that his wife will not join the club although she has been active in community services. "She won't join because she thinks it's still a men's club."