The Army committed unfair labor practices two years ago when it intervened at the request of the White House to help the Teamsters win a contentious union election among civilian employes at Fort Sill, Okla., the Federal Labor Relations Authority has ruled.

The intervention in the election, which was arranged by President Reagan's political director and the office of Defense Secretary Caspar W. Weinberger, violated a law requiring the government to remain neutral in union elections, according to the FLRA.

FLRA official Kenneth W. Goshorn said that under the ruling, which was made late last Friday, the election results will be thrown out and the secretary of the Army will be required to post notices for 60 days at Fort Sill admitting that he violated labor laws and promising not to repeat the violation. A new union election will be conducted, probably early next year, Goshorn said.

The Teamsters were the only major union to endorse Reagan in 1980 and 1984. Last year, the President's Commission on Organized Crime criticized the administration for its association with the Teamsters in light of the union's longtime ties to organized crime.

Two top Army officials had been accused by the FLRA's general counsel of violating federal labor law because they "breached the requirement of neutrality" by meeting at the Old Executive Office Building with Teamster officials a week before the 1985 election among 2,500 civilian workers at Fort Sill.

According to Army documents, just after the meeting, which was arranged by then White House political director Mitchell E. Daniels Jr., the Teamsters' circulated fliers at Fort Sill under the title: "When we talk for you, the White House listens."

The fliers described a two-hour meeting between the Teamsters and administration officials, and implied that the Army had agreed to consult more closely with workers before hiring private contractors to do part of the Army work. The key issue in the Fort Sill election was workers' fear that the use of outside contractors would lead to the loss of civilian jobs.

Daniels said last year that he was "misused" and misled by the Teamsters in setting up the meeting and that the administration at the time was unaware of the pending election at Fort Sill.

Teamsters President Jackie Presser, now awaiting trial on a criminal fraud indictment, had been scheduled to attend the White House meeting but did not.

The Teamsters won the election by a 591-to-516 vote over the incumbent union, the National Federation of Federal Employees (NFFE), which had represented civilian workers at Fort Sill for 15 years.

A memo written the day before the meeting by Army Col. James E. Schroeder to Deputy Assistant Secretary of the Army Valcris O. Ewell Jr. noted that the election was scheduled for Oct. 17 and said the gathering was intended to be a "show-the-flag meeting to impress Fort Sill's workers that the Teamsters can do more for them than the NFFE."

Steven Kreisberg, director of the NFFE's field operations, yesterday praised the FLRA's ruling, saying the 1985 action by the White House "was a clear show of favoritism toward the Teamsters." Eve Burton, a NFFE spokesman added, "The White House meeting was a payoff for the support the Teamsters gave the president."

A Teamsters spokesman could not be reached for comment yesterday.

At the time, the Teamsters represented about 600 civilian workers at Fort Sill, but were pushing to win the 2,500 employes that NFFE represented.

Goshorn said yesterday that it is "rare" for the FLRA to overturn the results of a union election, but in this case he said it was determined that no other remedy was available.

Kreisberg, who predicted the NFFE will win the new election, said he expects it to be held in February or March.