Libyan officials in Beirut are promoting a story that their government sent President Carter a $50,000 gift through his brother Billy, whose ties to the Libyans have been under investigation by the Justice Department.

[A White House spokesman said the president had received "no gifts from Libya, either directly or indirectly. The president to his knowledge has not been offered any such gift."]

Longtime observers here said that what made the Beirut reports newsworthy was not so much that they appeared in a minor newspaper known for its tries to the Syrian government, but that there was definite evidence that Libyan officials, who to date had not commented on the controversy surrounding Billy Carter's Libyan connections, had intentionally sought to leak the story through Beirut's always cooperative media.

Beirut's press is well-known for following the line of the government that provides financial support. Newspapers, however, also print stories reflecting the viewpoint of other governments that reward them financially.

There were no indications why the Libyans wanted to circulate the story that they had intended to send a gift to the president.

The story was offered by official Libyan sources to several newspapers (which turned it down) in the Lebanese capital this weekend, according to well-informed Lebanese. It was printed on the front page today of a minor daily, Ash Shraq, a pro-Syrian newspaper, which attributed it to its unnamed correspondent in Libya.

The newspaper's story gave neither the date when the alleged present was sent nor its exact nature beyond listing its worth. The newspaper offered no confirmation that the alleged present was ever received by President Carter.

The newspaper quoted Ahmed Tabib, identified as a senior civil servant in Libya's Foreign Relations Department in Tripoli, as the source for the revelation.

As Arabs we honor our guests and give them presents," Tabib was quoted as saying. "We gave gifts to all the members of the [Billy] Carter family, including President Jimmy Carter. The gift [to the president] worth $50,000 was sent with his brother."

"We actually have given these gifts to Billy Carter as a friend of the Libyan nation with whom we have close relations," the Libyan official was quoted as saying. "We thank him for his attitude in support of our cause and his efforts to strengthen relations between Libya and the American people."

The newspaper also quoted Tabib as confirming that the Libyans had made loans to Billy Carter under certain undetailed agreements and said that those loans were to be repaid.

The controversy around the president's brother began July 14 when Billy Carter registered with the Justice Department as a foreign agent and acknowledged receiving $220,000 from the Libyan government. Further disclosures about the extent of White House involvement with Billy Carter's dealings with the Libyans and the Justice Department have prompted a Senate inquiry that begins Monday.

The appearance of the story in a pro-Syrian newspaper, after at least one other more reputable and objective newspaper decided not to run it because it violated ground rules for receiving news stories from foreign government sources, had a certain logic, observers said.

Syria, like Libya, is opposed to the Camp David accords that seek a Middle East settlement. The publication of such an embarrassing allegation against President Carter, observers noted, could further damage the president's reelection chances and thus strike another blow against the controversial Camp David agreements.

"It is a big thing," noted one editor who had been approached by the Libyans to run the story. "They clearly want to blow it up."

The fact that the pro-Libyan newspaper in Beirut, As Safir, did not turn the story was interpreted by Beirut-based diplomats as a sign that the Libyans did not want to have the story directly attributed to their own controlled media.

The Libyan Embassy in Beirut refused to comment on the story, as did the United States Embassy, which learned of it only after journalists called to ask for the U.S. assessment.

U.S. officials expressed surprise at the story and observed that after Libya's long silence about connections with Billy Carter, the leak through Beirut seemed a rather "backhanded" way to discuss them.

Western diplomats, however, said the circuitous explanations resembled the way the Libyans do business. One diplomat in Beirut said. "It is in the nature of Arabs to send presents to the families of their friends and associates. That is how business is done in the Middle East."