Inflation and continuing demographic changes are like the pincers of a lobster's claw squeezing the Arlington education system, Superintendent Larry Cuban told 100 participants in an education forum Saturday.

"We're getting smaller and we are getting culturally diverse," Cuban said at the meeting sponsored by the Arlington County branches of the American Association for University Women, the League of Women Voters and the school system. But, he said, the cost of providing a quality education continues to rise.

Cuban said Arlington school enrollment has dropped by 10,000 students in the past decade. But the educational pressures have increased, he said, especially since Arlington has "almost two score" language groups who need special help in learning English as the basis for the rest of their education.

"Somehow people can't understand how if you have fewer students you can spend more," he said. But inflation has hit the schools hard, he said.

Later in the day, School Board Member Mary Margaret Whipple presented some information illustrating Cuban's points. She said that even though student population decrease, the school system still has certain fixed expenses, such as building maintenance and administrators' salaries.

Whipple said the schools receive almost 80 percent of their budget from county tax revenues. This year the county contribution represents 32 percent of the total county budget; for the 1971-72 school year more than 45 percent of the county budget went to schools, she said.

Whipple said that greater competition for the county tax dollar, especially for Metro construction and recreation programs, contributed to the smaller funding proportion.

Cuban said the decreasing enrollment and the financial crunch also have a psychological effect on the community and school personnel.

"No one likes the effect of getting smaller," he said. "There's no relationship between getting smaller and quality . . . yet people get that impression." It also has caused insecurity among the staff, he said.

Despite the problems, however, and given the "enormous social changes," he said, Arlington's "academic performance, by and large, has remained stable."

Cuban said there are "clear echos locally" of the national educational problems, concerns and trends described at the forum by Fenwick W. English, associate director of the American Association of School Administrators and director of the National Center for the Improvement of Learning.

Fenwick said schools are increasingly returning to more traditional curriculums and the public is putting a greater emphasis on competency. That emphasis has spurred more concern with skills, especially vocational skills at the secondary level, he said.

Parents also are becoming more militant and more sophisticated about the workings of their school systems, Fenwick said, which means they are holding the schools more accountable for educating children. He praised the parents in some bureacracy is the "slickest critter you're ever going to run across."

A third speaker at the forum, Richard Renfield, told the group that students are not being taught to think in school but, instead, are being forced to comply with a curriculum that may not interest them. Although the United States has done a "basically good job" in educating its students, there should be more freedom in the schools, Renfield said. He said he had developed a proposal for Fairfax schools that outlined an educational system based on student motivation. But school administrators decided against the plan last week.