WASHINGTON — On the opening day of a criminal trial testing the sweep of a federal law that regulates lobbying for foreign clients, defense lawyers argued that a prominent Washington lawyer accused of lying about his work for Ukraine’s government was in fact the victim of overzealous prosecutors.

They said the government had no evidence that the accused lawyer, Gregory B. Craig, had ever intended to deceive Justice Department officials who questioned him in 2012 and 2013 about his work for Ukraine. And they argued that the prosecution’s case was based on trivial misstatements he made in a brief letter and a 45-minute interview for which no notes exist.

“Errors are not criminal,” William W. Taylor III, one of Mr. Craig’s lawyers, argued in his opening statement at the trial in the United States District Court for the District of Columbia. Saying that Mr. Craig “has led an exemplary life,” Mr. Taylor added, “If there is one person whose honesty you would put your faith in, it’s Greg Craig.”

Mr. Craig, 74, is an influential Democratic Party figure who served as White House counsel in the Obama administration’s first year. He is accused of making false statements to federal officials who enforce the Foreign Agents Registration Act, a once-obscure law that requires the disclosure of efforts to influence policy or public opinion on behalf of certain foreign clients.