With the General Assembly winding down its work for 1985, the already feverish job of selling Citicorp and its bid for broad banking powers in Maryland moved into high gear today in the first of a round of key legislative hearings.

First came mention of the $250,000 that Citicorp, the largest bank in the country, annually gives to Maryland charities. Then a Citicorp executive harked back 87 years to the time his bank helped finance construction of the Baltimore and Ohio Railroad.

The photo albums were next, handsomely embossed folders filled with color pictures of beaming employes at Citicorp's giant credit card service center in South Dakota, a facility similar to the one the bank plans to build north of Hagerstown in exchange for the right to full banking privileges in Maryland by 1986.

For two hours, spokesmen for the New York bank, an aide to Gov. Harry Hughes and a former cabinet secretary urged members of the House Economic Matters Committee to approve legislation that would seal Hughes' agreement with Citicorp.

The new banking rules proposed by Hughes would allow out-of-state banks to open branches in Maryland after setting up limited services in the state for two years and promising to establish large offices in the 10 most economically depressed areas of the state. Under those rules, Citicorp -- which already offers limited services in Maryland -- would have a leg up on its competition and could open branches as early as July 1986.

Following Hughes' announcement of the agreement with Citicorp, Chase Manhattan Corp. and Chemical New York Corp., owners of the third and sixth largest banks in the country, filed applications to establish service in Maryland.

In recent days, critics of the new rules have complained that those regulations, which were devised with Citicorp in mind, violate a separate regional banking bill also pending in the legislature. Under that proposal, Maryland banks could enjoy four years of regional banking with 12 southeastern states and the District of Columbia before Maryland's borders would be opened to full interstate banking and competition by large institutions from New York and other money centers outside the proposed region.

Maryland Bankers Association lobbyist William K. Weaver, stepping up his campaign yesterday to derail the Citicorp legislation, derisively compared it to the Biblical "temptation of 30 pieces of silver."

Citicorp's promise to establish a 1,000-employe credit center near Hagerstown should never "involve a quid pro quo on banking legislation any more than any other power play before the General Assembly," said Weaver.

But Frank J. De Francis, Hughes' former economic development secretary, said, "The quid pro quo of 1,000 jobs . . . is the greatest good for the greatest number."

De Francis and Benjamin Bialek, Hughes' chief legislative aide, told the House committee that restrictions proposed by the governor would protect Maryland banks adequately from unfair competition from Citicorp or other out-of-state banks.

They said the key restriction, was one barring banks such as Citicorp from merging with or acquiring Maryland banks until 1989.

Citicorp's proposed $25 million facility mean "bricks and mortar and additional jobs around the state," Bialek said. "Is this so bad?"

Weaver and his allies countered, in part, by saying the Hagerstown facility would generate far fewer new jobs than advertised.

In addition, Reese Cropper, president of a bank on the Eastern Shore that has $85 million in assets, said he would never be able to persuade a bank like Citicorp -- which has more than $140 billion in assets -- to join with him in making small commercial loans in his community, as Baltimore banks do now.

The House committee will probably vote on the proposed new banking rules within two days, said vice chairman Casper R. Taylor Jr.