For those small congregations which aren't able to muster many volunteers for the Membership Committee, here is one that operates with just three leaders.

1. Greeting of Visitors - If there are just three people on a Membership Committee, put one of them in charge of recruiting teams to greet visitors on Sunday morning. Greeting and ushering is a small obligation that most people are willing to say yes to if someone else organizes it. It's an especially appropriate opportunity for new members. And visitors who are greeted well and have a good first impression, are more likely to stick around.
2. Put the second person in charge of the Caring Committee, if it is a part of Membership. The Caring Chairperson should be a delegator, calling others to do the specific Caring tasks that come along. Most everyone in a congregation is willing to prepare a meal, visit someone, provide a ride, if asked to do that one specific thing. So the Caring chairperson's responsibility is simply to be alert to needs and then find others to respond to them. The rewards are immense. Friends and members will overlook many of a congregation's shortcomings if they get an occasional phone call, note, or meal when they most need it.
3. The third person is the Chairperson. The chairperson devotes his or her time to organizing New UU classes and Membership Ceremonies, plus writing and/or ordering all of the print resources needed for Membership.