A defense contractor trying to keep an imperiled aircraft in production authorized payment of $25,000 to former White House aide Lyn Nofziger two days before Nofziger allegedly went to the White House to lobby to keep the plane alive.

Testifying at Nofziger's conflict-of-interest trial in federal court here, Thomas Guarino, former senior vice president of Fairchild Republic Corp., said he approved compensation for Nofziger's services following a dinner meeting with Nofziger and Washington lawyer Stanton D. Anderson Sept. 22, 1982.

The next day, Anderson's law firm gave Nofziger-Bragg Communications a check for $25,000. Then, according to the indictment, on Sept. 24, Nofziger made a presentation to staff members of the National Security Council in an effort to save the A10 antitank plane from extinction.

Anderson reportedly accompanied Nofziger to the meeting.

Anderson "said Mr. Nofziger would be a great help," Guarino recalled of his company's decision to enlist the former White House aide indirectly as a consultant to Anderson's law firm "on the A10."

Nofziger, who left the White House in January 1982, has been accused of illegal lobbying there on behalf of Fairchild and two other clients, the Wedtech Corp. and the Marine Engineers Beneficial Association (AFL-CIO).

Defense lawyers pointed out on cross-examination that Fairchild did not succeed in reversing a congressional decision in August 1982 to "zero-out" the A10. But Guarino pointed out that the company did manage to salvage some funds to cushion the blow.

NSC staff members present at the Sept. 24, 1982, meeting are expected to be called as prosecution witnesses next week. According to documents introduced into evidence, Fairchild paid $75,000 for Nofziger's services that year.

The other $50,000 came in two checks the company paid to the New American Foundation, an educational arm of the Citizens for the Republic of which Nofziger was chairman.

Guarino said Fairchild had been striving for months to save the A10 and hired Anderson in 1981 because "he knew these people" in the Reagan administration. The proposed Reagan budget that went to Congress in early 1982 included $350 million for the A10, enough to keep the production line open, but it was cut to zero by a Senate committee that summer.

Faced with the prospects of laying off 5,000 workers, Guarino said Fairchild decided to lobby several conservative House Republicans to support Reagan's embattled tax-hike bill in return for a reaffirmation of presidential support for the A10. The tax increase passed after strenuous White House lobbying among House Republicans that Nofziger directed for a two-week period at President Reagan's request. Budget director David A. Stockman reportedly engineered the deal by which Reagan reaffirmed his support for the A10 in an Aug. 20, 1982, note to Secretary of Defense Caspar W. Weinberger.

Guarino said it took him about a month to obtain a copy of the note and go lobbying at the Pentagon with it. "It was like a great egg hunt," he said. "No one could find a copy of it."

Earlier in the day, former White House aide James E. Jenkins concluded his testimony by saying that he helped Wedtech because "I felt I would be heavily criticized if I let that opportunity go by."

Jenkins, hired by Wedtech as a consultant in 1985 and paid $169,056 before he left in late 1986, was not asked who would have criticized him. As a White House aide, he said he decided to help the Bronx-based firm get financing for an Army engine contract as a personal project in May 1982 and was not aware until later that "anyone else" at the White House was interested in it.