The sounds of a soothing string quintet playing "Climb Every Mountain" bounced off the marble walls at the Corcoran Gallery last night--an appropriate arrival march for 200 high-rolling Democrats with surging hopes for 1982.

Those who purchased an entire table costing $10,000 for tonight's Democratic Congressional Dinner--as opposed to paying merely $1,000 for a single plate--got more than just the standard fruit cup. They were invited to last night's VIP reception at the Corcoran for some cold shrimp, tiny egg rolls and a chance to stand next to House Speaker Tip O'Neill.

And no one works a crowd like Tip O'Neill. Even if only for 15 minutes.

"Say hello to the speaker," Maurice Sonnenberg instructed his wife, Nina.

"You're doing a terrific job in Congress. Thank you," said Nina Sonnenberg, on cue.

"Thank you, darling," replied the speaker. He calls all the ladies darling.

Rushing out to his waiting car, O'Neill offered this assessment for the November elections: "It's going to be a great year. We're over our ills and weaknesses. We're better organized on the state and local level. We're doing much better."

The annual congressional dinner traditionally splits its pocketbook between the House and Senate campaign committees. Tonight's affair is expected to raise about $1.5 million for Democratic candidates and about 1,200 are expected to attend.

Some of the $10,000 and up donors include AT&T; General Electric; Life Underwriters; Goldman, Sachs and Co.; and Bob Strauss and Pamela Harriman, both of whom were at last night's party. Fifty members of the House and Senate were scheduled to show up. Fifteen was more like it.

But spirits were high.

"I'm going to raise $6 million this year," said Rep. Tony Coelho (D-Calif.), chairman of the Democratic Congressional Campaign Committee. "The highest we ever raised before is $1.5 million. We're definitely going to pick up some seats in the House."

"Anything's possible!" said Democratic National Committee Chairman Charles Manatt, assessing 1982. "How far down can the economy go? We're very encouraged. People are starting to realize just what Reaganomics is all about."

The harpsichord played on, and guests headed down the marble steps to waiting limos.