A Texas acquaintance of Democratic National Committee Chairman John C. White admitted in federal court in New York yesterday that he tried to con the Libyan government and fugitive financier Robert L. Vesco into believing he could bribe top Carter administration officials to release embargoed airplanes.

James C. Day, 48, a former state legislator who has a prior criminal record, pleaded guilty to conspiring to defraud the Libyan government in a $1 million scheme that included the use of an imposter for White and false claims that President Carter's top aide, Hamilton Jordon, had agreed to take part in the plot.

Day's plea yesterday was the first action resulting from a long-running grand jury investigation of the scheme. While Day's statements in open court exonerated Jordon, the court papers were less clear about White's role. c

Raymond Levites, the prosecutor in the case, said yesterday that the investigation is continuing.

White's attorney, Stuart Pierson, said yesterday that he was disappointed that the criminal information to which Day pleased guilty was not more emphatic about White's innocense. "Our position is that he wasn't implicated at all, and that he was a victim and not a participant," Pierson said of White.

Pierson said he still hopes for an affirmative exoneration of his client, who he said appeared before the New York grand jury twice, in October 1979 and last August.

White met with Libya's ambassador to the United Nations, Mansur Rashid Kikhia, in June 1979 at Day's request. The meeting at the Hotel Washington rooftop restaurant was photographed by the FBI.

According to the charges against Day he "did cause" White to "communicate" with senior State Department officers "regarding the status of certain embargoed aircraft and to discuss the possibility of a meeting between the Libyan ambassador to the United Nations and the president of the United States."

Pierson said that White made several calls to State Department officials about the Libyans' concern about aircraft they wanted. Libya had paid for eight C130s that were burned from delivery because the country was officially classified as a terrorist nation. Libyan officials also wanted to buy civilian airliners.

White talked with Deputy Secretary of State Warren Christopher after contacting Undersecretary David Newsom, an unidentified official, and possibly Assistant Secretary Harold Saunders, Pierson said. The attorney said White made the calls because Day asked him about the planes and about the possibility of a meeting between a Libyan envoy and President Carter or another high administration offical.

The idea of a meeting was rejected, Pierson said. None of the planes was released.

"In retrospect," Pierson said, White's intervention on Day's behalf "was probably not a very wise thing to do." Pierson explained that Day was not a friend of White but was influential in Democratic politics in Texas and was seen by White as someone who shouldn't be antagonized.

The New York grand jury investigation has been a politically sensitive matter for more than a year because of White's involvement. A Senate Judiciary subcommittee started an investigation of the matter and Sen. Orrin Hatch (R-Utah) was quoted just before the presidential election as saying that White "absolutely" was a "target" of the New York inquiry.

Pierson said yesterday that White House counsel Lloyd Cutler told White a few days before the election that he had heard from a reporter that the party chairman was about to be indicted. White and Pierson replied that the rumors were untrue. Cutler confirmed Pierson's account. Following President Carter's Nov. 4 defeat, White has said he will not seek reelection as party chairman.

According to the criminal charges against Day, Vesco gave him $8,000 to aid the scheme in April 1979. That was part of $30,000 Day took from various individuals promoting his efforts to get a contract with the Libyan government.

The court papers said Day "did falsely represent the nature and extent of the actions that John C. White would undertake to assist Day in his efforts on behalf of the Libyan government." For instance, Day falsely said that he had promised to pay White $14,000 to buy a car, the charges said.

As part of the conspiracy, Day arranged for a man named Alexander Phillips to impersonate White at a meeting with a Vesco representative in Washington, and to pass himself off as White's "executive assistant" at a meeting with Vesco in the Bahamas, the papers said.

Pierson said yesterday that the impostor blew his cover by admitting to Vesco that he didn't know Edward Bennett Williams, a prominent Washington attorney who had been treasurer of the DNC and who was Vesco's attorney.

In entering his plea before U.S. Dsitrict Court Judge Richard Owen yesterday, Day said: "I talked this thing over with my lawyer and concluded that my position was indefensible. . . . I misrepresented some facts to secure funds to pay the expenses to try to get a contract with the Libyan government."

The conspiracy Day pleaded guilty to began in September 1978 and continued for a year, when newspaper accounts revealed the investigation. In April 1978, Day pleaded guilty in federal court in Houston to making false statements to financial institutions to get loans. He received a two-year suspended sentence.

The same month he met with White in Washington and Vesco in the Bahamas.

One of the participants in the Vesco meeting was James Feeney, an undercover FBI informer and convicted con man whose tape recordings of conversations with Day, Vesco and others caused a big stir after they were obtained by Senate investigators and were made available to reporters.