Ronald C. Sprague, a financial consultant to a California farmer, said yesterday that Billy Carter dispatched him to Libya in March to help negotiate a $500,000 loan and a multimillion-dollar oil agreement, although Sprague said he knew nothing about Carter's financial liabilities and little about Libya, and had no experience in such business deals.

Testifying before a somewhat puzzled Senate investigative subcommittee, Sprague said his trip was paid for by his employer, George Belluomini of Bakersfield, Calif., whom he described as a "very, very close friend' of Billy Carter, Sprague said that Belluomini expected to receive a share of the oil deal.

Sprague said Billy Carter and Belluomini met several years ago when Carter visited Bakersfield to do a promotion for a women's softball team that included Belluomini's daughter.

Testimony, yesterday by Sprague and two oil company officials who expected to do business with the president's brother revealed new details of Billy Carter's unorthodox Libyan dealings, but offered no evidence of illegal activities that could damage President Carter's reelection campaign. Billy Carter is to testify today.

Sprague said that on March 17, the day he left for Libya, Billy Carter invited him to lunch at the White House. Sprague had his picture taken with the president, but said he did not discuss the Libyan trip with him and did not use the introduction to enhance his status when he was in Libya.

Like Henry R. (Randy) Coleman, an associate of Billy Carter who testified Tuesday, Sprague portrayed himself as a somewhat bewildered participant in the affair, an attitude that prompted Sen. Patrick J. Leahy (D-Vt.) to ridicule what he called the witnesses' "aw, shucks . . . Beverly Hillbillies" act.

"There's a streak of mendacity flowing through this which smells all the way back here," Leahy said. "If you ask me, it's simply a case of people saying, 'Here we've got a saleable name. Fortunately, it happens to be the same name as the president of the United States. . . . Let's get as much money out of this as we can.'"

Sprague disputed this interpretation, saying that the Libyans helped Billy Carter because he was their friend.

After his return from Libya, Sprague, at Billy Carter's request, sent urgent messages to Libyan officials trying to firm up Carter's loan. He was never told that Carter already had received $200,000 in two payments, through the Libyan Embassy here, he said.

About the first of July, Sprague said, he learned of the financial transactions from news accounts. When he called Coleman to ask why he had not been informed, he said he was told, "You weren't supposed to know." Sprague said he did not pursue the subject further, adding that Coleman "had no obligation to tell me."

Billy Carter did not get as good a deal from the Libyans as he had hoped, according to Sprague's testimony. Carter sent Sprague and Coleman to negotiate an unsecured 10-year "character loan" at 8.5 to 9 percent interest, Sprague said. Instead Mohammed Layas of the Libyan-Arab Foreign Bank would only agree to a secured five-year loan at 10 percent interest -- still a bargain at a time when the U.S. prime rate -- what banks charge their most creditworthy customers -- was in excess of 16 percent.

Sprague said Carter agreed to use his home and other real estate as collateral, but he did not inform the accountant of his considerable liabilities. No formal mortgage documents were ever drawn up in connection with the loan, Sprague said.

Sprague also said that the loan had no prepayment penalty, so that if the oil deal -- with commissions worth millions of dollars to Carter -- came through, Carter could pay back the loan immediately.

The deal to obtain 100,000 barrels per day of Libyan crude oil for the Florida-based Charter Oil Co. never materialized.

Sprague said he told the Libyans taht Carter "needed the money badly. He didn't have any money to pay off his bills."

The senators on the panel repeatedly suggested that the only reason Carter asked for the loan was because he felt he could wield influence as the president's brother.

"I've never known of a character loan for a half million dollars, and I have a lot of character," said Sen. Bob Dole (R-Kan.)

Sprague denied, however, that he and Coleman had received special treatment on their two-week trip. They arrived in Libya at night, he said, were not met at the airport, had no hotel reservations waiting and thus waited hours for a room, and "it wasn't much of a room."

"It was quite an experience," Strague said.

Several senators also suggested that the president might have known that Sprague was helping Billy Carter on his Libyan deals. Sprague's White House visit, Dole said, "had to be a pretty heady experience that put you in good stead with the Libyans. It opened a few doors while you were there."

Jack McGregor, a longtime friend of Billy Carter and a consultant to Charter Oil, speculated in testimony yesterday that the oil deal he helped Carter put together may have fallen through because the Libyans thought they had fulfilled their obligations to Carter through the loan.

McGregor said he understood that the Libyans were trying to help Billy Carter, not to gain influence over U.S. foreign policy, as some senators have suggested, but to compensate the president's brother for adverse publicity he received when he hosted a Libyan trade delegation to Georgia last year.

The publicity caused his income from public appearances -- his major source of revenue after financial problems with the peanut business -- to dry up.

McGregor said he was invited to the White House April 14 at Billy's Carter's request so that the president could thank him for helping persuade Billy to enter a Long Beach, Calif., naval hospital for treatment of alcoholism.

McGregor said the president seemed so pleased with his brother's progress that McGregor thought he might not be aware of his brother's financial problems. So McGregor said he told him: "Mr. President, you should know that I believe Billy is going to have some continuing financial problems after he leaves Long Beach, particularly if he must obtain legal representation for the developing investigation [into affairs of the Carter family peanut warehouse]. He may possibly require a legal defense fund, and I want you to know I intended to help in this record."

McGregor said he did not recall any response from the president.

Sen. Richard G. Lugar (R-Ind.) called McGregor's testimony "very important," because, as Lugar put it, from that point on the president "knew and had some idea of the vulnerability in which his brother had become involved."

Lewis I. Nasife, president of Charter Crude Oil, a subsidiary of Charter Oil, told the committee that he had never considered the letter of agreement with Billy Carter, in which he outlined the commission to be paid for Libyan oil, to be a firm contract. to be a firm contract.

Billy Carter repeatedly assured him that the oil deal would come through Nasife said, but in the past few months "due to changes in market conditions and his failure to produce the crude our contacts with Billy simply faded away. No monies or anything of value were ever paid by Charter to Billy Carter."

Nasife said he receives hundreds of telephone calls from individuals claiming to have access to Arab oil, but that Billy Carter's brokerage offer was the only one that he has ever followed up on. He said that was not because it involved the president's brother, but because Billy Carter had been recommended by McGregor and because discussions with Libyan attache Ali Houderi and officials of the Libyan National Oil Co. confirmed that Billy Carter had the political contacts in Libya that could lead to an oil agreement.