Peter Stefanou, a McLean, Va., accountant pleaded guilty today to tax evasion charges in U.S. District Court here. According to prosecutors, Stefanou worked for a London firm that sold hundreds of millions of dollars in phony tax shelters.

Stefanou admitted arranging fictitious commodity trades between Dominion Securities Group of McLean, in which he was a general partner, and London & Atlantic Market Brokers Ltd., a commodity brokerage house. Stefanou sold investments in the London firm's commodity contracts as tax shelters, receiving a fee equal to a percentage of the tax loss generated by the investments.

The documentation London & Atlantic provided his clients actually reflected rigged, prearranged and fictitious trades in metals commodity contracts, the government said in a criminal information filed against Stefanou today.

Stefanou admitted using some of these fraudulent deductions in preparing his personal income tax return in 1982 and a partnership tax return for Dominion in 1983.

Assistant U.S. Attorney Martin J. Auerbach said the case against Stefanou resulted from a continuing investigation of the tax shelter network created by Edward A. Markowitz, who pleaded guilty last year to creating almost $500 million in false and fraudulent tax deductions from 1979 to 1983. His victims included a long list of Hollywood and television personalities and professional athletes.

Beginning in 1980, Stefanou provided accounting services for a number of the Markowitz operations, based in New York and on L Street NW in Washington. Through the association with Markowitz, Stefanou obtained fraudulent tax losses for himself and his customers.

In 1982, Stefanou began using London & Atlantic as the source of tax shelters. That year, Dominion reported a fictitious loss of approximately $300,000 from fictitious trading activity with London & Atlantic, the government said.

As Dominion's general partner, Stefanou reported his share of the loss as a false deduction of $28,147 on his 1982 personal income tax return.

Stefanou, 33, is cooperating with prosecutors, the government said. He will be sentenced on July 9.