"This is quite neat," said Pamela Harriman, balancing a Miller beer plastic cup filled with water and her tortoise shell eyeglasses in one hand, leaving her other hand free to greet the guests. "These are Democrats who believe."

Nearly 400 strong young believers, mostly Capitol Hill staffers, a few politicians, like Sen. Chris Dodd (D-Conn.), and a few familiar Democratic faces walked through her drawing rooms and into the terraced garden last night to promote the idea of Democratic Party viability and support Harriman's political action committee, Democrats for the '80s. "My boss said to tell you," said Mike Stafford, an administrative assistant for Rep. Cec Heftel (D-Hawaii), "You are the first individual he has spoken with who seems to have grasped the nature of the problem and knows what to do."

Harriman enthusiastically demurred and then went to a microphone. With the gentle fire of the political stump, she spoke of the PAC's goals of balance, truth and substance and of her recent historical research. "I wanted to find out how Hoover was defeated in '32. One of the slogans was 'In Hoover we trusted and found we are busted.'"

The young audience cheered. Her husband, seasonless statesman Averell Harriman, introduced himself as an eyewitness to those events. "I know how it feels to be a Republican. I was one before 1928. I have had a hell of a lot more fun our of life being a Democrat."

What was most satisying about last night, said one staffer for the PAC, was that no one sent out invitations for the party. Only word of mouth and mimeographed notices attracted the crowd. "We all spread the gospel," said Bob Farber, a former Capitol Hill aide, now a consultant. Farber and a friend, consultant Jared Cameron, were catching up on Virginia state politics. "I think the Democrats have a good chance to win the governorships in Virginia and New Jersey, so those obits are not quite valid," said Cameron.

Since Pamela Harriman's formation of the PAC in December, six weeks after what her husband calls "the dismal event," she has hosted seven small dinners in her home, one regional dinner in Chicago and several informational meetings. Democrats for the '80s had raised $200,000 of its $1 million goal for 1981 before last night and has mounted one radio advertising campaign for Sen. Paul Sarbanes (D-Md.) against the National Conservative Political Action Committee.

Last night's gathering cost only $30 apiece for a buffet of meats, fruits and sweets and a concert by guitarist Charlie Byrd, who donated his services, instead of the $1,000 a plate for the previous sit-down dinners where former Carter Cabinet officers and current congressman have spoken. The appeal for money is critical, said Averell Harriman. "Last year the Republicans outspent the Democrats 6 to 1. Money can't do it all, but you can't do it without money."

Some of the guests were there out of morbid curiosity, or to declare formally that their post-election soul-searching was ended. "Well, I jokingly said this morning, I wanted to come to see what the Democrats looked like," said James Curlin, a former deputy assistant secretary of the interior for the Carter administration and now a newsletter editor. "There is a tremendous rebuilding job needed. It should be called Democrats for the '90s." Regina Mellon, a government affairs specialist for a private corporation, said, "I believe in what Mrs. Harriman is doing, and I wanted to see several people I hadn't seen since January 20."