The other night, Sen. H. John Heinz III (R-Pa.), who spent $2.5 million of his fortune to get elected, wined and dined 84 wealthy Republicans at his big house on O Street in Georgetown.

The Republicans were all members of something called "the Senate Trust," one of a burgeoning series of groups both political parties have set up to raise money. They were in Washington for the day to rub shoulders with the biggest GOP names in the U.S. Senate.

The Senate Trust is not the most elite of the groups , each of which offers access to the inner circles of government - for a price. Membership in it goes for $5,000 compared with the $10,000 it costs to become a Republican "Eagle."

But the trust is one of the most successful of the fund-raising efforts. Each of the last two years its 200 members have funnelled $1 million into Republican senatorial campaigns.

"We've met with a great response. We've gotten people involved who've never been involved in politics before," says Bob Moore, staff director of the Republican Senate Campaign Committee. "They like the interplay with the senators, the chance to sit down and talk with a real live senator."

The trust, and the other groups, represent a blending of mutual needs: the politician's need for campaign money, and the donor's desire to think he or she is getting something for the money.

In effect, it is an exercise in ego massage. A half-dozen times a year, donors to the trust get a chance to tell senators what they think is wrong with government, and the senators waht they think is wrong with governement, and the senators tell the donors what they are up to.

"What we've tried to do is form a group that can communicate its ideas to the Senate," said Howard Wilkins, a Wichita, Kan., businessman, who is chairman of the group. "I can't think of anything confidential any of us has learned out of this. "We're just keeping current. Our people put a premium on being current."

There is nothing particularly new about using access to government big shots or insider information to raise money. Political money men have been doing both legally and illegally for years.

The Democratic National Committee, for example, has what it calls a National Finance Council with a $5,000 admission. It offers quarterly meetings with administration heavyweights like presidential assistant Hamilton Jordan and Health, Education and Welfare Secretary Joseph A. Califano Jr. These are usually coupled with a reception at the White House with President Carter.

Democrats also have a President's Council which one enters after buying a $1,000 ticket to any fund-raising dinner featuring Jimmy Carter. Its smaller donors join something called "The President's Club," which entitles them to little more than the receipt of more fund-raising pleas. And when the president hosted a dinner party celebrating the Mideast treaty signing House solicited $1,000 donations from corporations that wanted to be represented at the historic event.

Republicans have their own series of groups. The elite of the elite is the GOP National Committee's 121-member Eagles Club with its $10,000 admission. It also has organizations called the Presidential Fund and Victory 1980.

A $1,000 contributor to the Presidential Fund becomes an "Elector" and gets a monthly newsletter and the telephone number to a special long-distance line to GOP chairman William Brock's office. For $500, a donor becomes a "Guardian" for $50, a "Patron," for $25 a "Sponsor," and for $15, simply a "Donor."

Victory 1980, as one might expect, has its own set of titles. A $2,500 donor to it becomes a "Victor", a $500 donor a "Challenger" and a $1,000 one an "Associate."

None of the groups, however, has quite the fine-tuned mechanism as the Senate Trust, with guarantees that all the money donated will go directly into Senate campaigns rather than overhead.

It also offers a greater degree of access to the party's congressional power center than any other group.

By the time trust members went to Heinz's house for dinner and cocktails last week, for example, they had spent more than a half-day in "for members only" briefings on Capitol Hill.

Senate Minority Leader Howard H. Baker Jr. (R-Tenn.) gave them an overview of what was going on in the Senate. Sen. Jacob Javits (R-N.Y.) talked to them about Mideast affairs, Sen. Henry Bellmon (R-Okla). about the federal budget, Sen. Mark O. Hatfield (R-Ore.) about energy policy and Sen. John Tower (R.Tex.) about the strategic arms limitation treaty.

In part, the groups, along with sophisticated direct mail operations both parties have developed, are a result of the campaign finance reforms of the 1970s which limit individual donations to $1,000 per campaign.

"Standard fund-raising has changed drastically in the last few years," says Wilkins of the Senate Trust. "A candidate can no longer depend on a handful of old time big givers to finance his campaign. He has tobroaden his base and identify new sources of money."

Republicans have been far more successful than Democrats in this effort. The Republican Senate Campaign Committee, for example, outraised its Democratic counterpart almost 7 to 1 last year, funneling $3.3 million into Senate campaigns.

Democrats attribute this to the Republican Party being the party of the wealthy. Wilkins attributes it to and "underdog" feeling. With Democrats outnumbering Republican 59 to 41 in the Senate, "We can't afford to have this imbalance go on much longer," he said. "It's something we can rally behind. We try harder because we have to."