About 185 women from the Boston area, decked out in purple and wearing all manner of red hats, will travel to Portland on Saturday aboard Amtrak's Downeaster train.

They plan to eat at Margarita's Restaurant downtown, where they will watch a fashion show of millinery, and visit the Old Port district.

The women are members of various chapters of the Red Hat Society, a national organization whose only requirement for membership is a red hat and a purple outfit.

The Red Hat Society got its start two years ago in California and already there are more than 1,700 chapters from Halifax, Nova Scotia to Anchorage, Alaska.

The society draws its inspiration from a poem by Jenny Johnson: ''Warning. When I Am An Old Woman, I Shall Wear Purple (with a red hat which doesn't go and doesn't suit me.)''

The women say they feel comfortable with an organization that has no committees to form, no agendas to set and no books to read. After leading l ong lives of service to family and others, they are glad to seem a little frivolous and to celebrate an older woman's right to just be.

''There are no rules in our organization. It's just a fun way for women to get together,'' says Sharyn Pulsifer of the Back Bay chapter, who organized the trip to Portland. She said she got the idea from a couple of different chapters in California and Texas which comandeered trains for an afternoon adventure.

''We're taking over the train,'' she says. ''It's a good way to sit and relax for a good length of time.''

Constance Loring, the ''Maine Goddess'' of the Royal River Chickadees, one of Maine's several Red Hat Society chapters, plans to meet the train with a fellow member.