The House of Delegates voted today to prohibit Maryland's retail stores and banks from charging membership fees for credit cards. The action, on an amendment to a bill that would raise interest rates on loans, was applauded by consumer groups as a major victory over the financial institutions that lobbied intensely in behalf of the legislation.

The 67-to-63 vote gave new verve to consumer advocates in the legislature who hope to see the entire interest-rate bill defeated when it comes to the House for a final vote, probably later this week.

The prohibition on membership fees means that state institutions that issue credit cards in Maryland will not be able to charge membership fees to the state's 1 million credit card holders.

The banking lobby had urged the legislature to allow membership fees by arguing that some banks were losing money on their credit card operations and needed higher interest rates and fees in order to recoup the losses. The state's largest bank, Maryland National, already has notified card holders that it has moved its credit card operation to Delaware and will impose an $18 yearly fee. The next two biggest banks, First National and Equitable, are planning to follow suit.

Legislators who supported the bid to allow credit card fees argued that the fees would be deducted from the monthly finance charges that some 60 percent of credit card holders currently pay.

"These membership fees would be uncontrolled," said Del. Steven V. Sklar (D-Baltimore), who sponsored a series of amendments aimed at watering down the measure. "People will refuse to renew their cards. It was an outrage in the community when banks announced membership fees. People began to cut up their cards."

The vote against credit card fees came during four hours of sharp debate that pitted Sklar and his allies against a harried Del. Fred C. Rummage (D-Prince George's). Rummage is chairman of the House Economic Matters Committee, which approved membership fees when it voted in favor of the interest-rate bill last week.

It was Rummage's second day defending the bill on the House floor, and it started badly. Del. Andrew Burns (D-Baltimore) opened the acrimonious debate by noting an embarrassing article in today's Baltimore Evening Sun that described how Rummage was coached on the bill yesterday by a colleague who received cues over the phone from a state official sitting with several loan company and banking lobbyists.

"Let me assure you that this phone is not connected with any lobbyist, nor was it," Rummage said at the outset of today's debate. "There has been no impropriety."

Among the lobbyists who sat with George L. Rayburn, an assistant commissioner of consumer credit, who was the state official who spoke by phone yesterday to Rummage's vice chairman, Caspar R. Taylor (D-Allegany), were William K. Weaver of the Maryland Bankers Association, John Devin Doolan of the Maryland Mortgage Bankers Association, and Charles H. Kresslein, a lobbyist for the Maryland Savings and Loan League.

Like much of the House leadership and the administration of Gov. Harry Hughes, Rummage was in the position today of defending a measure he vehemently opposed last year, a point that Sklar belabored throughout the day.

"What has changed since last year?" Sklar asked, reminding his colleagues that they had voted 101-to-14 in the 1981 session to prohibit credit card fees, and that advocates of this year's interest-rate deregulation, such as Rummage, Hughes, and Attorney General Stephen H. Sachs, had opposed such measures before.

Armed with graphs, charts, newspaper clippings, and a raft of statistics, Sklar coolly controlled the floor debate on the bill, which would allow the interest-rate ceiling to rise from 18 to 24 percent on most consumer loans and credit cards. His amendment to prohibit membership fees was one of 10 offered during the day that he said would strengthen consumer provisions in the bill and weaken financial advantages for the banks.

A final amendment offered by Sklar, one that would have repealed federal regulations that now apply in Maryland, failed by one vote. Sklar has argued repeatedly that the repeal is necessary to ensure that the bill's ceilings are enforceable.

The narrow votes on the amendments reflected the House members' general skepticism about raising interest rates and a general distrust of the banking community. Supporters of the bill, led by Rummage, could not muster more than 69 votes against Sklar and his allies, which some observers see as an ominous sign for the bill's future. At least 71 votes will be needed for its approval when it comes to the floor for a vote.