As President Carter walked out of the East Room last night, his nationally televised interrogation completed, a reporter asked him whether he felt he had finally put the Billy Carter affair behind him.

"I don't know," the president replied, barely breaking stride. "It depends on how you all handle it and how the American people judge it."

Actually, the president's goal last night was not to put the Billy Carter controversy behind him, but just put it in perspective.He went a long way toward accomplishing the goal because of a strong performance on his part and rather weak questioning by the reporters.

The controversy surrounding Billy Carter and his Libyan connection will percolate around the president throughout the rest of the political year, in congressional hearings and campaign oratory.

But the president, displaying a presence before the cameras that may well have been the envy of the opposition party's standard -- bearer, seemed to have made important gains in defusing the explosiveness of this scandal.

His defense rested on a personal appeal to family emotion, with emphasis on his concern for the hostages when he called on the services of his troubled brother as a diplomatic intermediary.

And all of this was what was needed most, as the president grappled with the controversy surrounding his brother. That is because what seems involved is not a scandal of the Watergate go-to-jail nature, but a controversy that centers around questions of poor judgment at the highest levels and of governing in a way that appeared sure to preserve the amateur standing of all involved.

In the end, the president admitted that, by using his brother as an intermediary, he may have been guilty of "bad judgment" -- which is what his political critics have long made the staple of their anti-Carter litany.

But he made it sound like a matter of political honor. ". . . I have enough judgment to know that that may have enhanced Billy's stature in the minds of the Libyans," the president said. "That's the only down side to it that I can understand, and that may have been bad judgment. But I was the one who made that judgment. I did what I thought was best for the country and best for the hostages and I believe that's exactly what Billy was doing." a

But he also said last night, when asked if he had thought that his brother was taking money from the Libyan government, that "yes, it occurred to me." However, questioners never followed up on that to ask just when it had occurred to him or whether he had ever asked his brother about it -- or even cautioned Billy against accepting money from the Libyans. a

Now those questions will most likely be put to him later in the campaign season, as the congressional inquiries continue and their political fallout remains.

The political implications of the Billy Carter controversy are a subject of deepest concern to the president and his closest advisers. The president's wife, Rosalynn, has spent recent days telephoning delegates and key Carter supporters around the country to assess the damage of the Libyan affair to her husband's prospects for renomination.

The First Lady, her husband, and his top advisers are concerned about the possibility that Sen. Henry Jackson (D-Wash.) may become a rallying point for center-right supporters of the president. They are especially concerned that a number of those supporters who are Jewish may have been so disillusioned by the revelations of Billy Carter's role as an intermediary with the radical Libyan government that they will bolt.

The prospect is unlikely. But within the Carter White House, there are those who think that Sen. Edward M. Kennedy (D-Mass.) is now so personally and bitterly anti-Carter that he would ask his delegates to cast their lot with Jackson supporters to deny Carter the nomination that he thought he had secured weeks ago.

And while the president avoided it in his televised performance last night, the chronology of the Billy Carter affair does not serve him well in his efforts to improve his poor standing with America's Jews.

The president, by his own admission, did not press his brother to drop all contact with the Libyans as soon as he heard of his brother's scheduled 1978 trip. In fact, after the trip, he sent Billy a copy of a State Department cable complimentary of the private mission, along with a note on how he had done a "good job."

It was not until late February 1979, the president said, that he had pressed Billy not to travel again to Libya, a country that has supported terrorists. This was only after his brother had caused him severe political embarrassment by saying that if American Jews did not like his traveling to Libya. "They can kiss my ass as far as I'm concerned now."

Political concerns were a large part of the president's thinking as he weighed the effects of the Billy Carter affair back in February 1979 -- and they were surely uppermost in his mind last night, as he sought to salvage his presidency with the Democratic National Convention that starts next week. But, as he found the questions put before him manageable, his own confidence clearly strengthened last night. He was nervous at the outset, his voice breaking in a high-pitched squeak when he said the word "Libya" in the opening moments. But by the end of the conference, he was deflecting questions with bits of humor and gentle persuasion.

Finally, at one point, he defended the use of his brother as a Libyan intermediary in the hostage crisis and the sending of his close relatives on other missions of ceremony and substance.

"I'm the one who made the decision, not my wife, or Dr. Brzezinski or any one else," he said of Billy's brief service as a diplomatic go-between. Of the larger role of his family in foreign affairs, he added: "That does not mean that all the members of my family have to be kept locked up in a closet."