In the White House mess -- that is a dining room, not a characterization -- the president's lawyers were taking a break from the Billy Carter affair for a quick, late lunch.

"If the president did not recall giving Billy cables, then I'm sure he did not give Billy any cables at all," said one of the lawyers, speaking with conviction. " . . . I mean, it is so highly unlikely.'

It was 2 p.m. Friday. After days of frantic scrambling, the White House counterparts felt they had finally gotten out in front on at least this aspect of the Billy Carter affair -- the question of those State Department cables about his trip to Libya.

Three-and-a-half hours later, a messenger delivered to Alfred H. Moses, one of the president's lawyers, a document that Billy Carter's attorney had sent over. It was a copy of a State Department cable, classified "confidential," that spoke favorably of Billy Carter's visit to Libya. In the upper right corner was a note, in the president's handwriting:

"To Billy, You did a good job under 'dry' circumstances (signed) Jimmy."

Moses was, as he would confide later, "startled." Clearly, the president had personally sent the document to his brother. And while the content was innocuous, and the wording even a little fatuous, the political implications of this latest development were far from good. The president had indeed done what he had told the world he had not recalled doing, and what his lawyers believed he had not done.

The case of the Libyan cables affords an important look at how the Carter White House has had to struggle to keep pace with the Billy Carter controversy. It has become a political albatross for the president on the eve of the Democratic National Convention that was to have conferred its certain presidential nomination upon him.

It shows two Washington lawyers of longstanding reputation -- White House counsel Lloyd Cutler and Moses -- thrust into the unaccustomed and legally unbecoming role of having to play beat-the-clock in order to put their cases together in time to get the White House side aired on the television network evening news.

It shows Atlanta attorney Charles Kirbo, the president's close friend, hovering in the background as Cutler and Moses went about their legal work, never obtrusive but always on hand to also represent the president's interests whenever crucial decisions were being made.

It shows the president's top officials scrambling to come up with basic information that was already in the hands of the Justice Department, two congressional committees and Billy Carter -- and being unable to do so for several days.

And mainly it shows how, when things are going badly for a beleaguered president, matters that would normally be considered just minor irritations can suddenly become incendiary.

The White House got the word through a rather indirect channel.

At 12:55 p.m. Wednesday, United Press International moved a story that quoted a Republican congressman, who was quoting a Justice Department report, which quoted statements that Billy Carter had allegedly made in a Justice Department interrogation.

Billy Carter reportedly had claimed that he had copies of State Department cables concerning Libya and that he had been given them, he said, by 'Jimmy."

The UPI asked the White House for comment on this development -- and that was how the president's advisers first heard of the matter.

Press secretary Jody Powell was taking the day off, and that left his deputy, Ray Jenkins, to handle the query, Jenkins called Powell and then he called Cutler.

"Everyone was aware that at some point we were going to have to take the matter to the president," Jenkins recalls, "But the problem was that we hardly knew what to talk to him about. We'd never had that FBI report. We knew only what was said in a wire service story about a Republican congressman who was relating what he said he saw in an FBI report that he did not have any more and which we had never seen."

Jenkins carried the UPI story upstairs to Cutler's office in the West Wing of the White House. Cutler, immediately conferred with Moses, who had recently joined the staff as the president's adviser on Jewish affairs and who had now been diverted to the role of cocounsel in this effort to make the complex Billy Carter affair explicable, if not totally manageable.

The president's attorneys had already been compiling documentation concerning Billy Carter and Libya, and that included copies of all cables on the subject in the White House files. "The notion that any cables had gotten into the possession of Billy Carter -- let alone that the president gave them to him -- never entered our minds," said one senior White House official.

The president's attorneys found that there were two cables in the files that the president's personal secretary, Susan Clough, kept for her boss. Neither bore the president's initials, although Carter has prided himself on meticulous record keeping and has made a habit of initialing every document he has read.

Shortly before 4 p.m., the two lawyers sent a message into the Cabinet Room, where the president was involved in a budget meeting, saying that they had to see him about an important new development. Carter quietly excused himself and met with Cutler and Moses.

The two lawyers told the president of the latest bad news that had broken in the affair of his brother -- the question of the cables -- and then they showed him copies of the only two they had found.

"I don't recall having shown or sent him a copy of these," the president told his lawyers, according to one knowledgeable official. The president went on to say that he remembered the substance of cables that had said Billy Carter's visit to Libya had gone well, and he recalled having told this to his brother.

It was late in the afternoon, and the conflicting concerns of the various Carter advisers began to come into play. The lawyers, Cutler, Moses and Cutler's deputy, Michael H. Cardozo, wanted the time to conduct a detailed search and interview all personnel; Jenkins kept impressing upon them the importance of answering the allegation in time for the network evening news.

There were seven cables, and all of them were innocuous. In Cutler's office, several advisers suggested the possibility of immediately making public their contents to show dramatically that this is not something of major diplomatic importance.

Cutler opposed the idea on the grounds that none of the president's attorneys knew just how to go about legally declassifying even such low-classification cables, and on the grounds that there might still be other cables that the White House did not know about but which Billy Carter might have in his possession.

As Cutler was drafting the statement that would be read to reporters, Kirbo appeared in his office. The president's close friend was just there, he said in his quiet and low-key way, to take a look at the draft. He made a few suggestions nodded his approval, and the deed was done.

Late in the afternoon -- just minutes before the deadline of the evening news -- Jenkins, sitting behind Powell's desk, read the statement to reporters. It contained the carefully worded phrase that the president "does not now recall" having shown his brother the cables or given them to him. Later, one of the White House lawyers would demur: "the word 'now' was actually just surplus in that phrase -- and if we'd had one more editing, we'd have taken out the 'now.'"

The story did not play well by White House assessments. On the television networks there was speculation about how, in Billy's hands, these cables -- so far unseen by anyone who was doing the talking -- could have enabled the Libyans to crack U.S. codes. And there was speculation of how the president might have broken laws designed to protect diplomatic secrets.

The next day, Thursday, Cutler and Moses began inquiring about the procedure to declassify the documents. It was not until mid-afternoon that they discovered that all of the cables had already been declassified more than a year earlier and that they had been turned over to columnist Jack Anderson under Freedom of Information Act procedures.

The same day, in a statement that promoted fast-acting relief at the Carter White House, Billy Carter told NBC News that actually he had no State Department cables and that his brother had never given him any.

Powell, back on the job, celebrated his return to action with unrestrained joy, as he presided over the distribution to reporters of the cables concerning the 1978 trip of Billy Carter to Libya, and revealed with flair how Anderson had them in his files all along.

Kirbo, his advisory presence not needed, was back in Atlanta that day. Cutler and Moses maintain that Kirbo operates strictly as an adviser plenipotentiary but without portfolio. He is not, the attorneys say, their boss, just their interested counselor.

"I do not have the feeling that Charles is calling the shots," says one of the lawyers. "He's not string-pulling. He just gives us a good feeling for the president and his thinking."

The White House officials were still feeling little pain from the cable controversy when, at 5:30 p.m., that messenger arrived from Billy Carter's lawyer, with the document that proved to be the smoking pea-shooter in the case of the Libya cables.

The president was over in the East Room, greeting 400 of his convention delegates and talking of victory in the fall, when Powell and Cutler walked over, cable in hand. The two men co-opted the office of the White House usher on the main floor of the mansion, and the president left the East Room to the sounds of enthusiastic applause and joined his advisers, who were in no mood to cheer.

The president, viewing his own written note to his brother, recalled he had mailed the cable to Plains. His secretary apparently had not made a copy for the president's files.

The president studied the cable in silence. But the document had been reproduced so many times his copy was illegible. It was already after 6 p.m., past the deadline of the news shows. Said Powell: "One of the things we've got to decide is if we should try to get this out today."

The president responded, according to Powell: "Don't even discuss it -- get it out today." This said, Carter walked out of the White House and climbed aboard a waiting helicopter that carried him to Camp David. During the weekend, all of his top advisers were to convene there for one last conference before he would make his full report to Congress and the nation about the Billy Carter affair.

In a couple of hours, the world would know that the president had indeed given his brother a cable -- but that the act was of no real consequence.

But the world would also know that the president, perhaps in a misguided gesture of support for an alcoholic and troubled brother, had chosen to praise Billy Carter for his contact with the Libyans rather than discourage him from further meetings with this nation that is the arms merchant of world terrorists. And this fact, in this political time, may prove to be the president's most difficult problem arising from the Billy Carter affair.

EPILOGUE: Upon arriving at Camp David Friday night, the president telephoned his press secretary and had him read the statement he was about to distribute to reporters. Carter made a couple of changes. The major one, Powell said, was that the president ordered his press secretary to fix a split infinitive.