Arlington School Superintendent Larry Cuban began his third annual press conference on the state of the county school system last week in a defensive stance.

"Despite newspaper headlines that would have readers believe the nation's public schools are chaotically run, rudderless and ineffective, the Arlington public schools have surely and steadily . . . improved."

Cuban has seen enough local headlines about Arlington schools to get his guard up this year. County Board chairman Walter Frankland and his Republican backed vice-chairman Stephen Detziler have been vocal critics of the school system and its leadership.

So it was with obvious enthusiasm that Cuban released the Academic Performance Report for 1979-80 which showed what he termed "almost dramatic improvement" in the school system.

"Some solid test improvement might make a good story given all the pessimistic news you hear about schools lately," suggested Cuban.

Most of the report contained results of standaridized achievement tests (SRA) in mathematics, English and social studies, given annually to grades 2, 4, 6, 8 and 11. This year's SRA scores equaled or exceeded last year's results at all grades tested.

The most dramatic improvement was achieved by sixth-graders in the mathematics test. Countywide scores improved by 12 points, placing the sixth-graders in the 77th percentile nationally. It was the highest score in the eight-year history of the standardized tests in Arlington.

The most disappointing results were those for minorities, particularly black students, who scored an average of more than 20 points below Arlington's white students on standardized tests.

Citing the lower scores as consistent with a national trend among black students, Cuban said it was important to identify the problem. "Now that it's on people's radar screens . . . we can re-double efforts to change that situation. It's going to take time."

Another set of scores include in the report were college extrance exams given to college bound seniors. Arlington's scores in 1979 were down six points in verbal and seven points in math when compared to 1978. But both scores were more than 30 points higher than the national average.

"I think any reasonable person looking a the data can reach only one conclusion," said Cuban. "Arlington schools are showing a steady improvement."