President Carter mailed his brother Billy a "confidential" State Department cable along with a note congratulating him for doing "a good job under the 'dry' circumstances" on his 1978 trip to Libya, the White House announced last night.

Press secretary Jody Powell told reporters at a hurriedly scheduled briefing that he did not think the action was improper or in any way encouraged Billy Carter's relationship with the Libyans.

Powell said the president's reference to "dry" circumstances apparently referred to the fact that Billy Carter, then a noted consumer of alcoholic beverages, was unable to drink in Libya, a strict Moslem country that serves no alcohol.

The cable was one of several the White House released Thursday in an effort to show the routine nature of the diplomatic cable traffic during Billy Carter's Libya visit. Powell said the president did not recall writing the note or sending the cable to his brother until a copy of it was delivered to the White House yesterday afternoon by Billy Carter's attorneys.

Some members of Congress who reviewed the Justice Department file on the foreign agent registration case against Billy Carter earlier this week charged that the president may have acted improperly in divulging classified material.

Last night's release is the latest flip-flop in the highly publicized story of Billy Carter and the State Department cables. Billy Carter told prosecutors in January that he had received such cables. On Thursday, he denied that, and yesterday he changed his story again to say that he had one cable.

In his latest account, which conformed with the White House version, Billy told a news conference in Georgia yesterday that the message, written by an American diplomat in Tripoli, said his 1978 visit had helped improve U.S. relations with Libya.

An FBI report of an interview with Billy Carter on Jan. 16, when he was under investigation for failing to register as a foreign agent, quoted him as having said he had a number of State Department cables about his visits and that "Jimmy gave them to me."

On Thursday, he denied that, saying: "I have State Department cables of nothing. Jimmy has shown me nothing."

Some hours before the White House announcement yesterday, however, Billy Carter said he did have one item. "I assume I got it from someone in the White House," he said, but he would not comment on whether it was his brother.

"It was over a year ago, and I don't remember," he said.

President Carter personally jotted down his compliments on the copy of the Oct. 1, 1978, cable.

Asked why on Thursday he had denied that he had gotten copies of any cables, Billy Carter said, "I didn't realize you were talking about it [the diplomat's memo]."

In its Oct. 1, 1978, cable on Billy Carter's trip to Libya, the embassy in Tripoli reported "no negative fallout" from the visit. "In fact, on the local scene we would rate it a very positive event which has opened some doors for this embassy and raised the morale of the American community," the cable said.

Powell said that Tom Beard, a White House liaison with the State Department, sent a note to the president's secretary, Susan Clough, about Oct. 11, 1978, presumably because the cable contained a favorable report about Billy Carter's trip.

The cable and President Carter's note were mailed to Billy Carter the same day. Powell said that the president, Clough and Beard did not remember the incident or the existence of the note until yesterday afternoon.

Alfred Moses, the White House official who is gathering material for congressional inquiries about the handling of the Billy Carter case, learned about the cable from Billy Carter's attorneys, Powell said. They delivered a copy to the White House after clearing it with the Justice Department, Powell added.

"Obviously the purpose of the note [from the president] wasn't to encourage any relationship between Billy and Libya," Powell said. "I think it would be more legitimate to interpret it as encouraging good and proper behavior." He noted that the White House had been concerned about the trip because of the sensitivity of Libyan-U.S. relations.

He also noted that the president has the authority to declassify information simply to relating it to someone, and the press secretary repeated White House statements of Thursday that the cables were "totally innocuous."

Earlier in the day, the Senate sub-committee headed by Birch Bayh (D-Ind.) met in executive session to discuss personnel for their investigation of Billy Carter's Libyan ties.

At a news conference after that meeting, Bayh denied that the panel was trying to "rush through" the inquiry, but he acknowledged that he wants to conclude it as far ahead of election day as possible.

"The closer we get to elections, the more difficult it is going to be for objective Republicans and Democrats to make objective decisions." Bayh told reporters yesterday. "That's a fact of life, and we cannot ignore it."

One subcommitee member, Sen. Max Baucus (D-Mont.), said, however, that he thought a politically attuned schedule to complete testimony from "all principal witnesses" by the end of August was much too ambitious.

"My personal feeling is that we're rushing it too much," Baucus warned in an interview. "This investigation should be totally blind to the political calendar."

So far, though, the nine-member subcommittee appears determined not to call President Carter next week despite public exhortations from the White House and private hints from Senate Majority leader Robert C. Byrd (D-W. Va.).

Byrd suggested to the committee's five Democrats at a meeting in Byrd's office Thursday afternoon that they take testimony from both the president and his brother before the start of the Democratic National Convention on Aug. 11.

"He [Byrd] wants it cleared up. He wanted to wrap it up one way or another as quickly as possible," said one source close to the inquiry into Billy Carter's ties to Libya.

At one point during the meeting with Byrd, sources said, several of the subcommittee's five Democrats seemed inclined to go along with the majority leader, but Bayh turned them around.

Baucus said the majority leader's approach was low-key.

"He did not push us," Baucus emphasized of the idea Byrd floated to call the Carters to the witness table within the next few days. "He just reported some of the things he'd heard, such as maybe it would be good to get everything out before the convention.

"We pointed out the problems with that approach. We're just not prepared," Baucus said.

Meanwhile, there were reports that backers of Sen. Edward M. Kennedy (D-Mass.) were also urging that the president or at least Billy Carter be called before the convention.

"We have felt pressure from a number of people with different motives, to call Billy or Jimmy next week," one source said. "But I don't think anybody in his right mind would consider calling Billy and not the president. And everybody [on the subcommittee] believes now is not the right time to call the president."

Powell indicated yesterday that the president is still waiting to be invited.

"No one's approached us," Powell told reporters. Asked whether the White House might approach the subcommittee, Powell said, "There's been no decision about [our] asking to go up there."

Once the Democratic convention is over, however, the subcommittee plans to press ahead as rapidly as possible, and to try to conclude its hearings by Labor Day.

"I don't think that's 'rushing through',"" Bayh insisted yesterday. He said he would call it "judicial speed."

Voicing his disagreement, Baucus said he thought the subcommittee members would come to realize that "We've got to do this thing right." He said he thought the investigation could last well beyond August, possibly even beyond the election.

In most congressional investigations of any magnitude, Baucus pointed out, laying the groundwork for the first public hearing usually takes months.

"You need painstaking examination of time logs, telephone logs, to know what questions to ask and what leads to pursue," he said.

Baucus said it might be best for the Democrats for any damaging revelations to come out earlier rather than later while the Republicans benefit if they came out close to the election. But he said he thought "the political consequences of a rush job" would be the most harmful to all.