When Jimmy Carter was here on May 1 to help raise money for the Montgomery County Democrats and to party with his White House staffers at the home of Gretchen Poston, his White House social secretary, he also did a little business for himself. At Bob Strauss' Watergate apartment the next day, he asked about 30 former Cabinet officers and top White House aides to help raise money to retire debts connected with his 1980 presidential campaign--about $1.25 million--and for the Democratic National Committee 1982 Special Unity campaign fund.

Carter asked each to contribute $5,000 and raise $10,000, although some there were of a fiscal magnitude that clearly more was expected of them. Some former Carterites report that the $5,000 has been scaled down to $2,500, however.

The Special Unity fund allows many who gave the maximum allowed by law to a candidate in 1980 to make their contribution to the DNC, which will pick up as much of the debt as the law allows, and help finance Democratic candidates this year. It is ecumenical--contributions are accepted from Kennedy supporters as well as Carter's.

To this end, the Democrats are having a $2,500-a-couple fund-raising dinner in Washington on Thursday. More than 200 people are expected, including Carter, Mondale, Strauss, former DNC chairman John White and Charles Manatt, the current national chairman.