Two brothers were convicted today of failing to pay about $1.5 million in state income tax over four years, in what prosecutors called the largest income tax evasion case in Maryland history.

"This is not even a close case," said Anne Arundel Circuit Judge Eugene M. Lerner as he convicted Dominick LaRosa, 44, and Joseph LaRosa, 40, both of Potomac. The brothers made a legitimate fortune buying and selling coal between 1981 and 1985, Lerner said, but then committed a crime by deliberately hiding their income to avoid taxes.

Dominick LaRosa, a former computer programmer with the Pentagon who was president of the coal company, could receive up to 70 years in prison when the brothers are sentenced Jan. 21. Joseph LaRosa, a comptroller with Weaver Brothers, a Chevy Chase real estate firm, could receive up to 90 years in prison. Both are free on their personal recognizance.

The $1.5 million in state tax was due on $20 million in profit that the LaRosas made selling coal to a West Virginia power plant. The LaRosas also did not pay an estimated $8 million in federal taxes during this period, state prosecutors said. Internal Revenue Service representatives attended the four-week trial, but no federal charges have been brought against the LaRosas.

Prosecutors said the brothers used some coal company money to buy personal items, including expensive homes and Mercedes-Benz cars, and that they bought about $1 million in stock. They did not declare the income in tax returns.

The LaRosas put much of their coal company profits, however, into $100,000 certificates of deposit, according to Assistant Attorney General Joseph L. Evans. The certificates were listed in the name of Dominick LaRosa, he said, and another name that was concocted. Sometimes a scrambled version of his wife's or mother's Social Security number would be used, Evans said. Interest from these accounts was not reported in tax returns.

In 1983, when the IRS inquired about accounts listed with legitimate Social Security numbers, the brothers created a company called Asoral, or LaRosa spelled backward, shifted their money into the company and invested it with Dean Whitter and E.F. Hutton.

The two brothers argued they were using a "Long Term Completed Contract" tax-paying method and intended to report their income and pay their taxes when their five-year coal contract ended this year. Company funds used for personal property were loans, they said.

But prosecutors said that this tax method should not apply to a business such as theirs. "This is not a quibble over accounting methods," Evans said, but "fraud on a massive scale."

Michael E. Marr, one of two attorneys for the LaRosas, argued in court that the brothers had trouble explaining their tax methods to investigators because of their difficulty with English and the affront they felt at the challenge to their integrity. The brothers emigrated from Italy in 1960.

"Me and my brother didn't do anything wrong," Dominick LaRosa told the judge after the convictions were announced. He said investigators were so eager to know where the money was that they didn't listen to his explanations. "Nobody wanted to know what we did or how we did it. I hope that God is up there to hear me."