Virginia Lt. Gov. Charles S. (Chuck) Robb, who supports the Equal Rights Amendment, has agreed to be the keynote speaker at the 100th anniversary celebration of a controversial Alexandria boat club that refuses to admit women as members.

The decision by Robb -- whose wife, Lynda Bird Johnson Robb, is head of the President's Advisory Committee on Women -- to speak at the all-male Old Dominion Boat Club on July 5, has drawn sharp protests from some members of Virginia's increasingly active women's movement.

"I'm appalled that Chuck Robb would go to the boat club once he realized it had a very limited clientele," said Partricia Winton Goodman, state coordinator for the 4,000-member Virginia chapter of the National Organization for Women (NOW). "I wonder why he would choose to cater to a small number of people rather than speak to the entire populace," she said.

"It certainly is surprising," said Lenny Burke, a member of NOW's Northern Virginia chapter. "Considering his past support of women's issues . . . I hope he changes his mind."

Rep. Herbert E. Harris II, a Democrat who represents Alexandria and Alexandria Mayor Charles E. Beatley, Jr., both refused to get involved with the 450-member boat club's celebration because of its refusal to admit women. Robb who lives in McLean, recently accepted the club's invitation to speak shortly before the traditional "Blessing of the Fleet" ceremony without knowing about the club's ban against women.

"We had no knowledge of their exclusionary policies," said David McCloud, Robb's executive assistant. "We thought this would be just a routine matter.

"The lieutenant governor speaks to a lot of groups that . . . he doesn't agree with, but he doesn't exclude them from his itinerary," McCloud said. He declined to name any.

Asked if Robb would now cancel the speech in view of the club's practices, McCloud said: "The lieutenant governor is not the kind of man to renege on a committment." He added that he did not know what Robb would have done if he had known about the club's policies.

It isn't the first time Robb has tangled with a faction of Virginians whose support he will need in his expected race for governor next year. Two years ago Robb infuriated blacks in the state by saying he believed President Carter should select federal judges from an all-white list of 10 male lawyers.

Lynda Bird Robb could not be reached for comment yesterday.

The boat club, which sits on a prime piece of waterfront real estate at the foot of King Street in the city's Old Town section, last April threw out two long-time members because they had proposed the name of local businesswoman Clarissa Brainard for membership.

The club has long been known as an unofficial headquarters for the city's "good ole boys," conservative businessmen who for years were influential in city politics and court circles. Until his resignation from office last year after two acquittals on gambling charges, former Alexandria prosecutor William L. Cowhig held his annual birthday parties there.

As a sign of its political power, the club for years refused to permit the public on an adjacent, city-owned block of King Street near the river, which it blocked off with a fence. The city council last year reopened the street by cutting the fence.

"Why is everyone making such bad publicity out of this?" asked club president George Ellmore yesterday. "We help needy children, we give money to charity, why is there such a fuss?" Ellmore refused to comment on the club's policies regarding minorities.

The White House said it was unable to confirm Ellmore's statement that it had sent a congratulatory message, but a White House press officer said, "We probably did. It's routine, who cares?"

An aide to Rep. Harris said, "We decided to it would be inappropriate to send a message in view of their policy of discrimination against women."

Stephanie Reed, former present of the Alexandria chapter of the League of Women Voters, sympathized with Robb's dilemma. "If he's really going to run for governor next year, he's got to make peace with a lot of people. He's their lieutenant governor, too, I guess" she said.