White House press secretary Jody Powell confessed yesterday that he commited an "inappropriate, regrettable and dumb" blunder in leaking suggestions to reporters that Sen. Charles H. Percy (R-Ill.) had made improper use of corporate aircraft and bank facilities.

Powell, who has been the administration's first line of public defense in the Bert Lance case, found himself for the first time a target of controversy as a result of the leak episode.

The press secretary said he called Percy, who has been one of the most agressive questioners in the Senate Governmental Affairs Committee's inquiry into the financial dealings of budget director Lance, to apologize for the incident. He added, with a chagrined smile, that President Carter agreed with his assessment of his behavior.

The Chicago Sun-Times reported that on Tuesday morning Powell called Loye W. Miller, the newspaper's Washington bureau chief, and said he had been told that Percy had regularly flown on an aircraft owned by Bell & Howell Co. and had failed to fully reimburse the First National Bank of Chicago for use of the bank's facilities during his 1972 campaign.

The use of aircraft belonging to two Georgia banks once headed by Lance is central to the controversy over Lance continued tenure as head of the Office of Management and Budget.

When Powell's information turned out to be unfounded, the Sun-Times decided to report his telephone call, characterizing it as "an apparent guerilla offensive aimed at discrediting" Percy, the ranking Republican on the Governmental Affairs Committee.

Lance, emphatically insisting that he will not resign is to testify before the committee today.

In a interview outside his Georgetown home yesterday as he left for work, Lance said.:

"If you can take allegations and innuendos and hearsay and everything else . . . and put them in the paper and show them on television and then say that's a fact . . . "And then, without having a chance to refute that and have my day in court, and be faced with the charge that because of that my effectiveness has been damaged and crippled, then we're in sad shape in this country."

It also was learned yesterday that Powell passed similar information on Percy to The New York Times, the Los Angeles Times and Cox newspapers, which publishes the Atlanta Constitution and Journal.Another unidentified White House official tipped off the Washington bureau of the Knight-Ridder newspaper that such rumors about Percy were being circulated.

Powell telephoned Percy yesterday morning to apologized, but not beforethere was a storm of protest over the incident from Democrats and Republicans on Capitol Hill.

Senate Majority Leader Robert C. Byrd (D-W. Va.) called Powell's action unfortunate and irresponsible. House Speaker Thomas P. (Tip) O'Neill Jr.'s only comment was "Being an Irishman, I'be never had much love or affection for informers."

Congressional Republicans seized on the incident to critize the entire White House handling of the Lance affair. Senate Minority Leader Howard H. Baker Jr. (R-Tenn.) said it "says something about the siege mentality of the White House," while Sen. H. John Heinz III (R-Pa.) compared it to the "dirty tricks" of the Nixon administration.

The exposure of Powell's leak episode, administration officials conceded, was certain to tarnish further not only his image but also that of the President in their attempts to defend Lance from the growing onslaught of allegations and demands for his resignation.

For one thing, the episode was a graphic public illustration that beneath his folksyGeorgia manner, Powell, like others of Carter's inner circle, is a tough political operative who relishes combat with the President's perceived political foes.

Moreover, the incident is likely to call into question the judgement of Powell and chief White House political adviser Hamilton Jordan, who, with the President, have been plotting administration strategy in the Lance case.

In an apparent attempt to demonstrate solidarity with his longtime colleague, Jordan yesterday made a rare appearance in the White House briefing room while Powell sought to explain his motives in the Percy leak.

At the same time, speculation in and around the White House began to shift away from the notion that Lance will resign after he appears before the Senate committee. One official, who a week ago thougt a prompt resignation was inevitable, noted Lance's extraordinarily jovial mood even in private and said, "All bats are off."

During the briefing, Powell insisted to skeptical snickers, that his calls to the news organizations were not an attempt to discredit Percy or motivated by partisan considerations. He said he passed on the information because it was "much in the public arena" recently and thought it would be of interest to reporters.

The press secretary also said he thought his role as the transmitter of the information would be kept confidential. But Miller, the Sun-Times bureau chief, who attended the briefing, disagreed. He said Powell set no "ground rules" in passing on the information.

None of the other news organizations published reports about the calls from Powell or the White House.

Powell steadfastly refused to identify his sources, but the instead the information did not result from the access to government data and confidential reports.

Under questioning, he said he did not recall other instances when he sought to pass on potentially embarrassing information about political figures. But some reporters said they recalled a similar attempt by Powell in connection with Rep. Morris K. Udall (D-Ariz.), a 1976 primary opponents of Carter's, during a battle this year over a water project in Udall's state.

Dressed in a short-sleeve white shirt, his tie loosened, Powell fell back on his sense of humor in attempting to make the best of what was clearly the worst public moment for him thus far in the administration. At the beginning of the briefing he said, "The GSA (General Services Administration) indicates they will be able to get sackcloth and ashes."

At one point, the press secretary seemed to suggest that he was considering resigning because of the episode. But, asked if he meant to give that impression, he said, "No,"