DES MOINES -- The tall and gray-haired Iowan wore a Simon button prominently displayed on her lapel. But as we passed in the Convention Center hallway, she smiled and flashed open her jacket. On the lining, there was a blue sticker revealing a very different allegiance: ''If only a woman were running.''

Such a yearning may have been widespread at the Women's Agenda Conference last weekend, but it was kept equally close to the vests of the 1,100 women who attended. This was a coming-together party for women who want to have an impact on the 1988 campaign.

Next fall, 10 million more women than men are expected to vote. The message the women here wanted to send to the candidates and the country was deliberately as deep as those grass roots and as widespread as the bipartisan membership of the 42 national women's groups that organized this event.

It was expressed this way by Sarah Harder, president of the American Association of University Women, in her warning to presidential candidates: ''Don't think of women's issues as a tiny handful of set-asides that will satisfy a rowdy minority.''

Indeed, in 1984, when presidential candidates and women's groups met, there was a simple script, a short checklist of issues and surefire applause lines. The men had only to mention the Equal Rights Amendment, the Democrats had only to nominate Geraldine Ferraro, and they considered the courtship complete.

''What we found out,'' said Ann Lewis, a Democratic adviser and longtime activist, as she looked back on 1984, ''is that not everybody felt included. The women working, juggling home and family, did not necessarily feel well represented by the agenda.''

Today the agenda is more inclusive and more complicated: a composite of jobs, housing, child care, health care, education and peace. At this meeting, the National Organization for Women, once the flagship of the women's movement, was just a wing of a larger and more moderate fleet. The issues were geared toward the bread-and-butter anxieties of women, their daily concerns about family life, children, the future.

''Women and men don't live in the same economic world,'' explained Celinda Lake of The Analysis Group, as she drew a portrait of the women's vote from her research. By and large, women are more pessimistic about the future, tend to frame larger issues in terms of their daily lives. They are less likely to feel that politicians are speaking their language. In the most general terms, she said, ''Women are looking for someone who understands their lives.''

Does the 1988 crop of candidates have that understanding? The five Democrats who came to the conference's Presidential Forum all appeared more comfortable with the audience and the issues than their predecessors were in 1984.

Of the group, Paul Simon's appeal was cast in the most narrow, even dated, terms: a checklist of Senate bills he cosponsored. The more successful messages -- those of Mike Dukakis and Bruce Babbitt -- integrated women's concerns into an essay answer rather than a list. Babbitt in particular spoke in a language that resonated with many women, ranging easily from the personal to the political.

The clear disappointment for women at this bipartisan conference was the total absence of the Republican candidates, who are still more worried about the party's right wing than its center. As Republican Ann Stone said unhappily, ''I'm afraid they thought they'd be walking into a lion's den.'' Bob Dole, who has a large constituency of moderate Republican women, was most notably missing.

But whether or not they ''understand women's lives,'' the candidates do understand votes. Women's votes have made the difference in 14 statewide races since 1984. Many candidates are struggling with the question, as one pollster put it, of ''how to sound presidential talking about day care.''

The conference here marked a very real transition for women in American politics. Women's issues today -- their economics lives, their families, their futures -- don't fit neatly on a bumper sticker the way the letters ''ERA'' once did. At the moment, the role of woman voters in the 1988 election is quite literally ''undecided.''