San Francisco — ''This is the greatest thing since sliced bread.'' Juanella Edwards, a delegate from Marietta, Ga., was being enthusiastic about the selection of Geraldine A. Ferraro as the vice-presidential nominee. ''My own daughters, who had no interest before, now want to work for the ticket,'' she went on. ''It's the biggest step ever taken in this nation.''
As the Democratic National Convention gets under way here, the Ferraro candidacy has created a palpable exuberance among delegates from Oregon to New Hampshire. It is an enthusiasm transcending personality or even partisan politics.
Women - all women - have surmounted another political barrier, and this shows on the faces of activists caucusing in hotel rooms and delegates crowding into the Moscone Center.
''Every woman in America stands taller today,'' says Lynn Cutler, vice-chairman of the Democratic National Committee.
''She'll add strength in Oklahoma because women have started to be active in politics there,'' comments Larry Uhl, delegate from Tulsa. ''It's a fantastic choice.''
Ann Richards, Texas state treasurer, remarks: ''We know that more young women are voting than men. So you'll see a registration effort and turnout you have never seen equaled before. It means women's political clout and voting power can only be enhanced.''
At the same time there is an awareness that the outcome of the election will turn in part on how Representative Ferraro handles herself. She is untried in the national arena. Party leaders say she has to avoid mistakes (such as impugning President Reagan's religiosity) and learn to say the right things.
''This as a watershed because Reagan is talking about a woman president in 1988, but whether the Democratic campaign is energized will be decided by how it goes from now on,'' comments Deralyn Davis, vice-chair of the Texas state party. ''We have a limited knowledge of her. Is she a good speaker? You have to weigh every word with a balance machine.''
Whatever direction the campaign takes, the choice of a woman vice-presidential candidate is viewed as an inevitable development. It follows decades of steady, if often fitful, progress in the emancipation of women, socially and civilly.
Why now? Political experts see a number of forces converging:
* The phenomenal surge of women into the labor force. More than 50 percent hold jobs.
* The growing presence of women in political life. Since 1975 the number of women holding positions at all levels of government has more than doubled. Ten years ago only 4 percent of all elected officials - from local city councils and state legislatures to Congress - comprised women. Today that figure is over 10 percent.
* For the first time since they obtained the vote, women in 1980 voted in equal proportion to men (about 59 percent of those registered). Because women are the majority of the population, this means more women are voting than men.
* In 1980, women for the first time tended to vote differently than men. Hence the much-talked-about gender gap - the fact that Mr. Reagan has more support among men than women.
''Historically women and men have never voted differently,'' says Kathy Stanwick of the Center for American Women and Politics at Rutgers University. ''So women are emerging as an independent force.''
Ironically, the last Democratic convention actually had more women delegates. This is because the party, in a reform designed to make the nomination process more disciplined, this time enlarged the number of convention superdelegates - members of Congress, governors, and others who are delegates by virtue of their office. (There are 35 governors, for example, but only one woman governor). But the state delegations are evenly divided between men and women.
Also, the permanent chair of the convention is a woman - Kentucky Gov. Martha Layne Collins. Representative Ferraro was chair of the platform committee. And Rosalind Wyman is chair and chief exeuctive officer of the convention planning committee.
Republicans too have their feminists and battlers for women's rights. And as Ms. Ferraro gears up for the hustings, they are pointing up the contribution, past and present, the Republican Party has made to advancing women politically.
''This is not a watershed thing but a transition over a decade,'' says Betty Heitman, co-chairman of the Republican National Committee. ''Women are really coming into their own, entering into politics in greater numbers and definitely on the way up.''
This election will find both parties fighting for the soul of women. The Republicans are confident women will vote the pocketbook issues - and pick Reagan.
''Women remember life under Jimmy Carter as the terrible inflation, high interest rates, and the President telling people to tighten their belts,'' Mrs. Heitman says. ''Women have seen a turnaround under Reagan.''
The Democrats argue the President's policies have pauperized many families and benefited mostly the rich. And while he has appointed women to high office, they say, he has been slow in supporting reform of pension laws and other measures aimed at helping women. His opposition to an equal rights amendment and his foreign policies also come under Democratic attack.
Although Ms. Ferraro is also expected to boost Democratic votes among Roman Catholic and ethnic communities, her gender has visibly galvanized the interest of women.
''This has energized us,'' says Mrs. Richards. ''It makes us realize we have something at stake.''