A group of liberal Maryland legislators, searching for new sources of state income to make up for U.S. budget cuts, think they have come up with the perfect plan: increase taxes on 16 large oil companies that do business in the state.

Faced with mounting opposition from the firms involved, these legislators say that three bills introduced this year would "close loopholes for oil companies" and increase state revenues by nearly $50 million, providing needed dollars for the state's fledgling transportation fund and social service programs that are losing money under the Reagan administration's economic plan.

Although unlikely to pass, the legislation represents an increasing effort on the part of liberal legislators to strengthen the state treasury by using new powers granted states under Reagan's "new federalism," particularly in the area of corporate taxation. By changing federal law that Maryland automatically copies, President Reagan's tax plan will reduce by $40 million corporate tax revenues that the state formerly used for transportation projects.

The oil companies, some of which earned profits exceeding $20 billion last year are not pleased. Tax specialists, attorneys, and public relations officers from Shell, Texaco, Gulf, Amoco, and Exxon came to a public hearing today to brand the proposed legislation discriminatory. They argued that the existing tax exemptions are legitimate business deductions that are also available to other industries.

One bill, similar to legislation enacted in Minnesota and Wisconsin, would prohibit oil companies from deducting "windfall profits" taxes from their taxable income, reversing a federal regulation that went into effect automatically in Maryland in 1980. A second bill would prevent deductions for drilling oil and gas wells. The third measure, perhaps the most controversial, would provide $36 million in state revenues next year by forcing oil companies to pay taxes on gross receipts and report income from other holdings.

The corporate representatives argued that Maryland would suffer from these new taxes because oil companies would be induced to move to other states.

Del. Stewart Bainum, Jr. (D.-Montgomery) chided the oil companies for their soaring profits. He said 14 of the 16 companies affected by the windfall tax legislation rank in the top 50 in the world in corporate earnings.

"The question is," Bainum told his colleagues on the House Ways and Means committee, "do we want to give $20 million to 16 of the world's largest corporations who do not even reside in the state, or to people who have been victimized by federal cuts?"