Have no idea what line of work you're in or what your situation is. I tried with a couple of employers to get to a part-time situation but it never worked out. In watching friends who had successfully negotiated part-time arrangements, it seems they often got dragged back to full-time, at least for extended periods. ("We really need you to step up for this project, etc.")
I have one friend who teaches courses for a federal agency on a contract basis. When he is teaching a class, it's full-time for the duration (3 days, a week, two weeks.) But he can turn down offers of classes to teach and during those periods he isn't working at all. The thing I like about his situation is the classes don't get extended as a project does when it runs into trouble.
Good luck with your attempt!