His friends call them misstatements. His critics call them lies.

Either way, the continuing indications that Billy Carter misled government investigators, the news media and the public about his ties to Libya have left the president's brother with a ballooning credibility problem.

The gap between Billy Carter's account and what others say is the truth yawned wider Wednesday when Joel Lisker, head of the Justice Department's foreign agents registration unit, flatly accused Billy Carter of lying when he denied in a Jan. 16 interview that he had received money from the Libyan government.

But the history of Billy Carter's controversial association with Libya is riddled with misstatements -- or lies. At times he has contradicted even himself, saying one thing one day and then something else a short time later.

Critics might call this a cover-up. Friends would be more disposed to say that such inconsistencies are part of Billy Carter's offhand nature. one way or the other, here are some of the inconsistencies:

Item: Billy Carter repeatedly denied ever speaking to his brother about the Libyan controversy. "I have not talked to Jimmy about it at all," he told a television interviewer on July 15.

Two days later, President Carter told reporters in Florida: "Just a few days ago, I recommended to Billy that he go ahead and make a complete revelation of what happened to the Justice Department."

On July 22, Billy Carter acknowledged in a television interview that the president had called him "a couple or three weeks ago."

Item: Billy Carter has repeatedly denied that the Libyans wanted any political favors. "The Libyans never asked me for anything -- nothing whatsoever," he said in Georgia last week.

Last month, however, an Atlanta real estate developer who accompanied Carter on his 1978 trip to Libya said officials there brought up President Carter's refusal to let Libya import eight U.S.-built C130 cargo planes. The Libyans did so despite prior agreement not to talk about political issues, developer Thomas Jordan said.

Item: Billy Carter has publicly stated that he has made no efforts to exercise political influence on behalf of the Libyans.

But he told Justice Department officials in January that he called White House appointments secretary Philip J. Wise Jr. last year to talk about the planes, according to Lisker, Wise says he cannot recall the conversation but acknowledged, through a spokesman, speaking to Billy Carter's friend, Henry (Randy) Coleman, who accompanied the president's brother to Libya.

Justice Department records also show that Billy Carter refused to tell investigators whether he had made any attempts to influence the president, directly or through their mother, Lillian, to release the planes, according to members of Congress who have seen the files.

Item: Billy Carter reportedly has said he called Wise 300 to 400 times during the last four years to relate problems of citizens who have encountered problems with government bureaucracy.

But White House press secretary Jody Powell, speaking for Wise, yesterday said: "Phil has no record of any number of calls from Billy approaching 300 or 400 or even 100."

Item: Before agreeing to register as a Libyan foreign agent, Billy Carter repeatedly denied, both publicly and to Justice Department investigators, that he had received any money from the Libyans.

After denying during the Jan. 16 interview that he had received any payments, Billy Carter told investigators on June 11 that the $20,000 he deposited on Dec. 31 was a reimbursement for expenses incurred while escorting a Libyan delegation around the country, according to Justice Department records.

In his registration statement, filed with Lisker's office last month, Carter described the total of $220,000 the Libyans gave him as part of a $500,000 loan.

Item: Before registering as a foreign agent, Billy Carter said he made two trips to Libya and invited a Libyan delegation here only because he was friends with officials of that nation. He denied that he was profiting from the relationship.

But in his registration statement, Billy Carter acknowledged offering to negotiate an increased allotment of Libyan oil for the Florida-based Charter Oil Co. If successful in doing so, he could have earned commissions totaling millions of dollars.

In addition, Atlanta developer Jordan said those who went on the trip to Libya planned to form a corporation to arrange a broad range of trade between the United States and Libya. Such trade also could have earned the partners in the company millions, Jordan said, and Billy Carter was to receive 40 percent, the largest share of the profits.