Ronald Reagan acknowledged today that he made a mistake when he told a Nebraska audience Wednesday night that Vietnam war veterans are "not eligible for the G.I. Bill of Rights with regard to education or anything."

The error raised anew the issue of Reagan's factual flubs which his opponents and even some of his aides believe could become a significant factor in the campaign. At an airport runway press conference under a cold rain, Reagan took notice of press preoccupation with his misstatement and termed it "journalistic incest."

Reagan blamed his inaccurate statement about veterans' benefits on two high-ranking retired military officers. He decline to identify them, but members of his staff said Reagan was referring to Adm. Thomas H. Moorer, former chairman of the Joint Chiefs of Staff, and Edward Rowney, a retired three-star general who sometimes advises the former California governor. Both men met with Reagan when he was in Washington earlier this week.

Neither Moorer nor Rowney could be reached for comment.

The mistake put Reagan somewhat on the defensive when he arrived here to campaign in the Pennsylvania primary, where he faces a determined challenge by George Bush.

Reagan was peppered with questions about a variety of alleged misstatements, including an inaccurate comment he once made that the nation's most-renowned chief justice, John Marshall, had not been a lawyer.

Responding with some heat to one question, Reagan took issue with a recent CBS program "about my so-called facts," and said that a CBS statement that President Carter has increased the federal payroll by only 6,000 employes is incorrect. Reagan has used different figures to describe the size of the federal payroll increase, sometimes as high as 131,000, but he said today that the correct number probably was 43,000.

When asked whether he was saying his figures had been accurate, Reagan replied: "Not entirely, but more correct than CBS."

Reagan did not attempt to defend the accuracy of his comment that Vietnam veterans are ineligible for eduational and other benefits. Under current law Vietnam era veterans may receive educational benefits for 10 years after separation from service and are eligible for government-subsidized home loans the rest of their lives.

"I've been getting complaints from Vietnam veterans almost every place I've gone that they are not getting the comparable benefits that have always gone to the various veterans . . ." Reagan said. "Both of these gentlemen [Moorer and Rowney] indicated that they [the veterans] were not getting the G.I. Bill and I in good faith took their word and stated that. Evidently, that was not quite correct."

Tonight, Reagan conferred with his advisers about his misstatement on Vietnam veterans benefits and called in reporters who had been covering the campaign to tell them how the mistake had originated.

Reagan said Rowney and Moorer, whom he did not identify by name, had been talking about the lack of educational benefits for members of the all-volunteer regular Army while he had been assuming that they were responding to his questions about benefits for Vietnam veterans. As a result of this "double-track conversation, Reagan said he left the meeting "shocked and horrified" in the belief that Vietnam veterans were being denied federally sponsored educational benefits.

Reagan made the misstatement at a reception at the Riverside Golf Club in Grand Island, Neb., and repeated it later in a slightly different version before an overflow crowd at a Reagan-for-president dinner.

On the flight today from Grand Island to Pittsburgh, Reagan's aides did not appear to be troubled about the inaccuracy. Instead, they concentrated on putting out a statement which corrected what Reagan believes to be a misperception of his position on the Olympic boycott.

In that statement, issued by aides while the candidate was making a closed-door speech here at the Duquesne Club, Reagan said he favored a boycott of the Summer Olympic Games in Moscow but did not think President Carter should use "Soviet-style coercion" to deny U.S. athletes their passports.

"If the president cannot persuade the athletes to stay away from Moscow, he has only himself to blame," Reagan said.

The emphasis of both Reagan and the press on correcting previous statements produced some uneasiness among Reagan aides in Pennsylvania.

"We're going to win the primary here anyway," one of them said, "but I sure hope he's not doing this in October."

Slips have dogged Reagan this week as he campaigned in Texas and Nebraska. In Lubbock, he referred to Sen. Edward M. Kennedy as "Sen. Massachusetts." And in Grand Island he took issue with "the myth" that the Repulbican Party was "the country club and board room party."

He made his statement in a Grand Island country club.