WASHINGTON — Elizabeth Edwards, the wife of Democratic presidential candidate John Edwards, is writing a letter to her children so they will have her guidance after she is no longer with them.

Ms. Edwards, who announced in March that her breast cancer had returned in an incurable form, said she came up with the idea 20 years ago after watching the movie “Terms of Endearment,” where the mother knew she was dying and wrote to her children.

“So I started writing it then long before I knew, of course, of any cancer,” Ms. Edwards said. “And it just tells them the things I hope that they’ll know about growing up. I know they’d have their father as a great moral guide, but of course, there’s no mother who doesn’t want to get her two cents in.”

Ms. Edwards said her advice to her three children — Cate, 25, Emma Claire, 9, and Jack, 7 — include such things as what type of people they should marry and the kind of church they should go to.

“You don’t know when your time’s going to come and whether you’re going to have any warning, and it would be a great idea to pass on the things you thought would be important to them,” she said.

Ms. Edwards, who has been receiving treatments while her husband, the former North Carolina senator, campaigns, said she’s “doing great” and feeling strong.

“I still have my hair so that’s a good sign, and it doesn’t exhaust me in any way. That’s also great news. I can campaign,” Ms. Edwards said.