A Beechcraft King Air 200 airplane used by Bert Lance wile he ran two different Georgia banks changed hands in two unusual transactions now under study by the criminal fraud section of the Justice Department, the comptroller of the currency confirmed yesterday.

The airplane once belonged to the Calhoun First National Bank, was transferred to a partnership controlled by Lance and his wife, LaBelle, then was transferred to the National Bank of Georgia in Atlanta, where Lance became president in January, 1975, according to Sen. Charles H. Percy (R-Ill.). John G. Heimann, the comptroller, confirmed this at a Senate hearing.

Informed sources said yesterday that the private use of aircraft ostensibly owned by the banks Lance ran will prove one of themost damaging elements in the Lance affair when the full facts are made known. The sources indicated that there seem to have been hundreds of instances when Lance used bank-owned aircraft for trips that had no evident connection with bank business.

The Justice Department is now studying the results of a detailed investigation of the airplane matter prepared by the comptroller's bank examiners, who reportedly spend many hours trying to decipher incomplete flight logs and other evidence.

Percy raised a new potential accusation against Lance yesterday - that he may have deliberately backdated three checks less than a month before be joined the Carter administration to gain a tax benefit.

A spokesman of Lance in Washington flatly denied any backdating of checks.

Percy said that if the checks were not deliberately backdated, but were actually written on the dates that they carry, then Lance wrote checks for a total of $196,426.69 on a day when he had a total of $27,732.55 in his bank accounts.

Percy's analysis of these checks was based on information contained in the latest report on Lance's finances prepared by the comptroller's office and released this week.

The report shows that Lance wrote five checks on his Calhoun account - checks numbered 917 through 921 - but either wrote them out of order or backdated three of them. Checks 917 and 918 were dated Jan. 7, 1977, while numbers 919, 920 and 921 were dated Dec. 31.

These latter three were all made out to the Chemical and First National City banks in New York to repay principal and interest on outstanding loans to Lance. Interest payments are tax deductible, and Percy raised the possibility yesterday that Lance dated the checks Dec. 31 (they were written in his own hand) to claim the interest deduction on his 1976 income tax returns.

The comptroller's report shows that the checks dated Dec. 31 were not actually paid by his Calhoun bank until the 13th, 14th and 15th of January. By that time Lance had more than adequate funds either in Calhoun or Atlanta to cover the checks.

But on Dec. 31 his accounts contined nearly $170,000 too little to cover the checks.

"Where was that money going to come from?" Percy asked Comptroller Heimann yesterday at a hearing of the Senate Governmental Affairs Committee.

"Senate, that's a good question," the comptroller replied.

A spolesman for Lance said that Lance's interest deductions for 1976 were based on information provided by the banks to whom the interest was paid, not on the dates of his checks.

The spokesman quoted Lance as saying he was looking forward to responding to Percy when he testifies next Thursday.

Sources knowledgeable about the investigations into Lance's affairs said later that this matter could probally only be cleared up if Lance would tell the committee exactly what his cash flow situation was in late 1976 and early 1977. But one key source said that Lance's financial dealings are so convoluted that it would probably be best for him to resign rather than produce a full explanation of the flow of his funds.

In his second day of testimony before the Senate committee. Heimann went a few inches further than he did Thursday in criticizing Lance's behavior as a banker. At one point, for example, he said that federal bank examiners viewed Lance's overdrafts at the Calhoun bank in 1972-75 "terribly seriously." And Heimann confirmed explicitly that those overdrafts represented a "serious violation" of the banking laws.

Heimann also said that on matters involving Lance that his office has referred to the Justice Department for possible prosecution, "I don't believe that we've acted frivolously."

In Lance's defense, Heimann said: "To my knowledge he did not knowingly break the law."

Heimann was asked to comment on one sensitive new area for Lance but avoided the question carefully. This involves Lance's $3.435 million loan from the First National Bank of Chicago, on which Lance has had to post new collateral as recently as this week, according to Percy.

Lance testified in July that that loan was "fully collateralized," though the comptroller's report of Aug. 18 shows that originally, $1.625 million of the loan was in the form of an unsecured note.

Informed official sources said last night that Lance's testimony did not conform to the facts, but that it might have been accidental.

In another development yesterday,the former U.S. attorney in Atlanta, who dropped an investigation into some of Lance's affairs one day before Lance was appointed director of the Office of Management and Budget, charged the Carter administration with hiding details of Lance's past from the Senate when he was confirmed.

The former prosecutor, John W. Stokes, a Republican, claimed the FBI must have discovered embarrassing facts about Lance last December which were not passed on to the Senate. But he offered no evidence to support this charge.

Another lawyer, Bobby Lee Cook, came to Washington yesterday to say that his former client, convicted embezzler Bill Lee Campbell, had made incredible, untrue charges against Lance.

According to the Atlanda Constitution, Campbell has told Senate investigators that Lance was a party to his embezzlements from the Calhoun First National Bank, for which he is now serving an eight year jail sentence.

His former attorney said no such accusation had ever been made previously, although it would have helped Campbell to be able to implicate Lance when Campbell's case was being prosecuted.