Maryland state Sen. Robert J. Garagiola  talks with supporters as he kicks off his congressional campaign last fall. (Katherine Frey/THE WASHINGTON POST)

Maryland state Sen. Robert J. Garagiola may have violated state ethics rules by failing to report his employment by a D.C. lobbying firm on financial disclosure forms for three consecutive years.

Garagiola (D-Montgomery) is currently the state Senate majority leader and is embroiled in a heated contest for the Democratic nomination to take on Rep. Roscoe G. Bartlett (R) in a congressional district redrawn to be competitive in November. The campaign of financier John Delaney, Garagiola’s opponent in the primary, alerted the news media this week to Garagiola’s omissions, alleging that he had “lied to the voters.”

At the time Garagiola was elected to the Senate in 2002, he was working as a lobbyist for the firm Greenberg Traurig. Yet on forms he had to file from 2001 to 2003 as a state Senate candidate and then as a member of the Senate, Garagiola did not report that he had any outside employment.

Garagiola’s tax returns, which he previously provided to The Washington Post, tell another story. In 2002, Garagiola made $119,000 at Greenberg Traurig, and the firm paid him $78,000 in 2003.

The General Assembly’s Ethics Guide states that members must disclose “[s]ources of the legislator’s earned income . . . and that of the legislator’s immediate family, including employment or businesses,” and the disclosure forms from the years in question ask legislators whether they “received a salary or was sole or partial owner of a business entity from which earned income was received.” Garagiola checked the “No” box.

Garagiola’s campaign said the omission of his Greenberg Traurig employment stemmed from the way the lawmaker, an attorney, read the disclosure forms at the time. Garagiola understood at least one set of instructions as saying he only needed to disclose outside income if he owned a business.

Without addressing Garagiola’s case specifically, Michael Lord, the executive director of the Maryland State Ethics Commission, said he “could see where an interpretation could be made that to satisfy the reporting requirements you have to both earn an income and be an owner of a business. But that’s not advice we would give if asked.”

The wording of the form was slightly altered in 2007, and Garagiola since then has disclosed his outside employment with the Rockville law firm Stein Sperling Bennet De Jong Driscoll.

“The Ethics Commission had never noted an issue, and if they request, we certainly will amend as requested,” said Garagiola campaign manager Sean Rankin. “But we do find it ironic that John Delaney, who still has not released his personal financial disclosure form or his taxes, raised such a charge: maybe Delaney should follow his own advice and stop hiding his financial statements and taxes. What is he hiding? Another Andy Harris-like situation?”

The Garagiola campaign has sought for weeks to make Delaney’s wealth an issue by challenging him to release his tax returns, the way opponents of former Massachusetts governor Mitt Romney (R) have in the Republican presidential primaries.

Delaney released a very basic summary of his tax returns to The Post this month but not the actual forms. He is due next month to file the financial disclosure form required of all congressional candidates, after receiving an extension.

Garagiola’s camp has also sought to make hay of the fact that Delaney contributed to the congressional campaign of Rep. Andy Harris (R-Md.), who ousted Democratic congressman Frank M. Kratovil Jr. in 2010. Delaney has not explained that donation, although his campaign has emphasized his long history of raising money for Democratic candidates and causes.

For his part, Delaney has sought to portray Garagiola as a Washington insider trying to hide his lobbyist past.

Garagiola’s past work for Greenberg Traurig was not secret. Records on file with the U.S. Senate show that he was a registered lobbyist for the firm, representing more than a dozen clients in the health-care field from 1999 through 2003.

But neither Garagiola’s official state Senate biography — which runs to nearly 700 words and lists dozens of current and past affiliations — nor the biography on his congressional campaign Web site make any mention of his work for Greenberg Traurig.

Staff writer Greg Masters contributed to this report.