The District’s new ethics panel unanimously approved Tuesday a preliminary investigation of D.C. Council member Jim Graham’s conduct on a land deal four years ago, when he allegedly mingled his council role with his service on the Metro board.

In one of its first inquiries since being impaneled Oct. 1, the three-member Board of Ethics and Government Accountability will begin compiling information about whether Graham may have violated council or District ethics rules while serving on the Metro board in 2008, officials said.

If the ethics panel concludes there is a “reasonable basis” that Graham violated District ethics rules, a formal probe will be launched and the council member will be allowed to defend himself before the board, said Robert J. Spagnoletti, the board’s chairman.

“We are just at the beginning phases of all of this,” said Deborah Lathen, a board member.

The board’s decision comes less than a week after an independent report commissioned by Metro concluded that Graham (D-Ward 1) violated the transit authority’s ethics rules by trying to influence Metro’s plans for a vacant lot on Florida Avenue NW.

The report, which cost Metro $800,000, alleges that Graham intermingled his council duties with Metro responsibilities by attempting to tie the land deal to the city’s lottery contract.

The Metro investigation did not uncover any evidence that Graham broke any laws, and Graham has denied any wrongdoing. But in recent days, several newspaper columnists and civic activists have pressed for the new ethics board to look into the matter.

In an interview after learning of the ethics board’s decision, Graham vowed to cooperate fully but questioned whether further scrutiny of the matter is needed.

“All of the essential facts are known,” said Graham, who served as the D.C. Council designee to the Metro board from 1999 to 2010. “You have a law firm who spent $800,000 of public funds to uncover every aspect of this. To have another investigation, I don’t know why.”

Spagnoletti, a former D.C. attorney general, said the board has a “responsibility” to follow through on allegations of improper conduct.

“When there is an allegation a council member has potentially violated the District of Columbia Code of Conduct, we are responsible for conducting a preliminary investigation,” Spagnoletti said.

For about two years, Graham has been faced with questions about whether he improperly intervened when Banneker Ventures sought to develop the Metro-owned land on Florida Avenue near the Shaw-Howard Metro station. Banneker expressed an interest in the project about the same time that Warren Williams Jr., a principal at Banneker, was seeking a lucrative contract to run the D.C. Lottery.

The Metro report, conducted by the law firm of Cadwalader, Wickersham & Taft, concluded that Graham told Banneker officials in 2008 he would support the lottery bid if they dropped their Metro plans.

Graham has stated he didn’t think Banneker was financially qualified for the Metro project, but has denied linking his concern to the lottery bid.

“I have no recollection of the comment being made, and I have said that over and over again,” Graham said Tuesday. “And if it was made, it was made in a very offhand way.”

In 2009, the D.C. Council approved rules requiring members to have “complete independence or impartiality” and to avoid conflicts that could be viewed as “affecting adversely the confidence of the public in the integrity of government.”

Although those rules were enacted after the allegation against Graham, Spagnoletti said council members are also expected to abide by the broader ethics guidelines outlined in the District’s personnel manual for city employees.

Under the 2011 law establishing the ethics panel, the board can look into alleged misconduct dating back as many as five years, Spagnoletti said.

Mike DeBonis and Lori Aratani contributed to this report.