The Prince George's County school board has severly restricted the organizing efforts of the American Federation of Teacher (AFTI) in the county's public schools, just as the union was starting a major campaign to increase its membership in the Washington area.

The surprise late-night vote Thursday followed discussions of the issue in closed-door sessions and behind-the-scenes pressure by the Prince George's County Educators Association, the politically influential bargaining unit for most of the school system's teachers and administrators.

The board voted to rescind a four-year-old policy that permitted AFT access to teacher's lounges for the purpose of distributing literature because the educator's association invoked a provision in its contract giving the incumbent union exclusive access to the schools during school hours.

Although the open lounge policy was adopted in 1975, it was only this year that the association begain to feel the challenge to its dominance and objected to AFTI's access. The AFT drive in Prince George's has resulted in an increase in membership from 800 last year to 1,250 this year, officials of the AFL-CIO affiliate said. The association claims about 6,000 members, making it the largest union of county workers.

Walter Levin, general counsel for the association said yesterday, "the negotiated agreement (contract) provides that we can use the schools for organizing and that no other union can. We just insisted that they observe the contracts."

Teachers who belong to the AFT can still distribute literature in their own schools, but professional union organzers are barred from school during school hours, Levin said.

"If you have the schools as a union battleground, you aren't going to be doing any teaching," he said. "If they can get enough signatures to request a union election, then there are different rules for a campaign," he said. AFT must obtain signatures from 20 percent of the teachers in order to request an election contesting the association's role as bargaining agent, he said.

Mary Ellen Shunk, AFT's representative in Prince George's, yesterday criticized the board's vote to restrict her union from the schools. "It's a matter of elementary fairness," she said. "The PGCEA (the association) has been in power and wants to maintain the status quo. It's a union fight, and the board is aiding one side over the other, or why should they have discussed the issue beforehand in closed session. I have yet to be notified that the issue is even being discussed.

In the last 10 years, the association has developed a strong political base in Prince George's County and is particularly powerful in school board elections. In 1980, six of the board's nine members are coming up for re-election.

School board members said yesterday they voted to curtail AFT's access because of the conflict with the contract negotiated by the association this year and not because they were trying to restrict AFT's membership drive.

"It was felt that the policy seemed to convey a preferential treatment to one employee organization, the AFT," said board member, A. James Golato. He added none of the school system's other unions representing non-teaching staff can go into the schools and organize. The association, however, has the right to enter the schools as the elected representative of the teachers, he said.

"If one organization doesn't have teachers in the school to spread the world for it, that's too bad," Golato said. "We don't have any responsibility to put weights on the feet of the better dancers."

Our feelings were that those rooms (teacher's lounges) should not be used as tax-subsidized rooms for organizing," he said.

Lesley Kreimer, the board member who sponsored the 1975 policy giving the AFT access, said yesterday that AFT organizers can still distribute literature after school and through school mail boxes and can hold afterhours meetings without causing the board to violate the contract.

"They still have their First Amendment rights," she said. "They just can't send the troops in any more."