Averell and Pamela Harriman opened their exquisite Georgetown home last night, replete with van Goghs, Picassos and Renoirs, to several busloads of Democratic hopefuls. They were in town for a "training conference." The buses, limousines and receiving line jammed the cobblestone street.

One woman brought her pocket camera and posed in front of the wall portrait of senior statesman Harriman. Another woman accidentally ground her name tag into the thick white carpet. A butler was quite upset.

And one document--rich in political ammunition--served as a conversation piece for part of the evening. Officials at the Democratic National Committee were circulating a five-page memo originated by the Republican Policy Committee. It listed the names and addresses of all the sponsors of CBS' hard-hitting documentary "People Like Us," which aired Wednesday, on the "victims" of the Reagan administrations budget cuts, as well as a detailed Republican defense. The idea was to encourage Republicans to complain to the sponsors. And the Democrats were gloating that the Republicans were on the run.

The entire evening was a learning experience.

The Teachers: the Democratic National Committee Training Conference, Wednesday through today, for congressional challengers. Last night's party for 400 was the social highlight of the conference. Yesterday, Sen. Edward M. Kennedy (D-Mass.), Pamela Harriman and Sen. Gary Hart (D-Colo.) taught. Today, DNC chairman Charles Manatt is scheduled to share his wisdom.

The Students: About 160 House and Senate challengers from 31 states, most of whom wore navy blue pin-stripe suits, light blue shirts, cranberry ties and collar pins. White collars optional. Shirtwaist silk dresses were the uniform for women candidates. There were some reruns like Herb Harris from Virginia and Pete Kostmayer from Pennsylvania. But most of them were newcomers.

"We don't have cocktail parties like this in Kansas," said Linda Slattery, who husband, Jim, is running for the House.

"No, we sure don't," said the candidate, who grew up in Good Intentions, Kan.

They plan to find housing outside the District if elected.

"I figure Maryland, Virgina, Kansas--it's all the same suburbia," said Jim Slattery.

The Aide: A person who comes to the conference for a challenger who decided to stay in New Jersey. Like Alexander Kaplen. Twenty-two. Harvard graduate.

"Wanna hear a story about a really bizarre candidate?" said Kaplen. "I work for Howard Rosen from New Jersey, and this guy actually goes out and does blue-collar jobs, two, three days a week. At first people were suspicious of him. But now they invite him to their home."

Kaplen is Rosen's "issues man."

The Prey: Dozens of lobbyists who were even more popular than the ham and salmon. Like Joe Beeman of the American Federation of State, County and Municipal Employees, which has $800,000 to spend this year. He figures at least 15 candidates approached him for money or union backing last night. "The money is nice, but sometimes the votes are more important to these folks," he said.

The plumbers, the bricklayers, the ladies' garment workers, the auto workers and the service employes were also quite in demand.

Toy of the Night: A paper gun called The Reagan Raygun. When the trigger is pulled, a picture of Reagan pops out surrounded by the words "Trust Me." It had Pamela Harriman, Chuck Manatt and Rep. Tony Coelho (D-Calif.) in hysterics.