Baltimore Mayor Sheila Dixon's legal defense received a boost yesterday from the city Law Department, less than a week after her indictment on public corruption charges.

A two-page letter from the department, headed by a Dixon appointee, said a list of companies doing business with the city fails to meet technical requirements laid out in city ethics laws.

That conclusion is consistent with arguments last week by Dixon's attorney, who said charges that she accepted gifts from a city developer and failed to report them wouldn't stick, in part because the city did not keep a list of eligible companies as required.

Dixon's attorney Arnold M. Weiner viewed the letter as a victory. "It confirms that everything I said was accurate," he said. But the determination undermines the long-standing practices of the Ethics Board, which helps elected and appointed officials avoid conflicts of interest by making available the names of businesses that have received checks from the city in a given calendar year.

Dixon is charged with four counts of perjury for failing to report thousands of dollars in gifts from Ronald H. Lipscomb, a developer who has worked on projects that have received millions in city tax breaks. His company, Doracon, is currently on the list of companies used by the Ethics Board.

Weiner argued in an unusual televised news conference last week that Dixon did not need to report the gifts, in part, because no certified list existed for her to check.

Confusion over what constitutes a proper list has broad implications. It raises the possibility that hundreds of city workers who file disclosure forms can claim ignorance as to whether gifts they received were from companies that do business with the city.

In a letter dated yesterday to Dixon's attorneys, the city Law Department found:

•The list used by the Ethics Board was not valid because it was not certified by the city finance director.

• The companies included on the list did not necessarily meet the definition of companies doing business with the city as outlined in the ethics code.

• Dixon, who was City Council president during the period in question, did not have a password to access the finance department database on which the list is kept.

Dixon's attorneys requested the written ruling after questions emerged this week about whether a database of vendors available through a city intranet fulfills the requirement for a certified list spelled out in the city's code, said the City Solicitor George A. Nilson.

The ruling, a letter from the Law Department, was signed by Deputy City Solicitor Donald R. Huskey.

Weiner contended last week that Dixon's disclosure forms are "100 percent accurate" and that the four perjury counts she faces are "based upon a monstrous legal mistake."

State Prosecutor Robert A. Rohrbaugh alleges that Lipscomb gave Dixon lavish gifts, including a $2,000 gift certificate at a local furrier, airplane tickets and clothing from Giorgio Armani and St. John Boutique. Rohrbaugh has not commented on the case.

Dixon said she was dating Lipscomb when she received the gifts. She was also voting on millions of dollars in tax breaks that went to city projects in which Lipscomb had a financial stake.

For example, prosecutors noted in court papers that Dixon and Lipscomb left for a trip to New York the same day that she voted on the Board of Estimates to approve a $13.6 million tax break for a project developed in part by Lipscomb.

But Weiner argued that the definition of "doing business" with the city is so "technical" that the lack of an accurate list would make it difficult for an official such as Dixon to know whether the gifts she received needed to be reported.

"How is a public official supposed to know whether an entity is doing business with a city and therefore has to be listed on its forms?" Weiner asked at the news conference.