On June 21, 1977, Rep. John M.Murphy (D-N.Y.), chairman of the House Merchant Marine Committee, held a cocktail party fund-raiser at the Mayflower Hotel.

It was like many other such events, except for the timing. It was not an election year and Murphy had no large campaign debt to pay off.

But it was in the middle of hearings before Murphy's committee on a cargo preference bill that would have benefited the maritime industry, and of the $30,000 Murphy raised at the party, $9,930 came from the maritime industry and maritime unions.

THe Murphy fundraiser is cited in a 112-page booklet put out by Common Cause and released yesterday called "How Mobet Talks in Congress."

A Common Cause release said the study "is designed to demonstrate the various ways in which political contributions, financial holdings, honoraria, outside earnings, gifts and lobbying expenditures affect government decisions that impact on the lives of all Americans."

In the case of special-interest contributions, Common Cause says, "The message is clear: Special-interest money pouring into political campaigns is contributing to legislative paralysis and interest group domination of Congress."

To back up that contention, the study reports:

Twenty-four of the 31 Merchant Marine committee members who voted for the cargo preference bill, which was eventually defeated on the House floor, received a total of $82,263 in campaign contributions from maritime unions during their 1976 races. Murphy got a total of $11,200; Rep. Leo Zeferetti (D-N.Y.) got $18,138, and Rep. Marion Biaggi (D-N.Y.) got $6,800.

To the members of the House Commerce Committee, where a bill to contain risinf hospital costs was defeated by one vote, the American Medical Association made contributions totalling $101,259 since 1975. During that period, Rep. Robert Krueger (D-Tex.) got $17,050, Rep. Tim Lee Carter (R-Ky.) got $10,000, and Rep. Sam Devine (R-Ohio), $10,100.

Nineteen of the 22 Commerce Committee members who voted to kill hospital cost containment received $85,150, while 16 who voted for the bill received $16,109.

Thirty-two of the 36 members of the House Education and Labor committee got more than $500,000 from labor over a three-year period.

Thirty-eight of the 46 House Agriculture Committee members got $381,631 from dairy groups in the same period. Twelve of 18 senators on the Senate Agriculture Committee got $100,000 from dairy groups in their last campaigns.

Two-thirds of the campaign money spent by 15 powerful House committee chairment in the last election came from interest groups.

"While substantial campaign contributions may not actually 'buy' votes, they do ensure easy access to public officials and create an unhealthy atmosphere of familiarity," the study said.

The public lobbying group suggested public financing of congressional campaigns, a step it has been pushing hard on Capito Hill, as a remedy to the special-interest contribution problem.

Since public financing was enacted for presidential campaigns, interest groups have poured money into congressional campaigns, with the total increasing from $12.5 million in 1974 in $22.6 million in 1976. By the middle of this year, the groups had spent $10.9 million, and $27 million more was available for the fall elections.

The study also contends that the private holdings of a member of Congress can lead to a conflict of conflict of interest.Rep. Cecil Heftel (D-Hawaii) holds all or a part of two television stations and a radio station and receives a salary of $21,649 each-three months from a newspaper conglomerate. In 1977, Heftel introduced four bills to make it more difficult for pay and cable television 'companies to compete with broadcast stations. Common Cause suggested strengthening rules disqualifying members from voting on subjects in which they have a financial interest