A five-year program of stressing basic educational goals such as reading and arithmetic in the Arlington schools was credited yesterday with significantly improving the reading and mathematics test scores of elementary students.

The average reading scores of Arlington second graders on the tests have climbed steadily from the 49th percentile in the 1973-1974 school year to the 60th percentile this year, school officials noted in releasing the test scores. A ranking in the 60th percentile means that the score was higher than 60 percent of the students nationwide who took the test. A change of five percentile points at the elementary level and eight at the secondary level is considered significant by school officials.

Reading scores for fourth graders rose from the 48th to the 73rd percentile. Results from sixth, eighth and 11th graders remained fairly stable.

In math the second graders' score climbed from the 52nd to the 68th percentile over the last four years. Fourth graders went from the 42nd to the 64th percentile, while sixth graders increased from the 43rd to the 67th percentile. Eighth and 11th grade scores remained fairly constant.

For the first time, Arlington compared the current test results of a class against scores recorded by the same class in earlier years.

That comparison shows that the national standing of Arlington's high school juniors in language arts and science has declined from well above to slightly below national averages since that class was in the sixth grade.

The national ranking of that class has slipped from the 57th to 46th percentile in language arts and from 61st to 47th percentile in science.

School Superintendent Larry Cuban said that an expository writing program has been offered to improve writing skills. He said the school system also would like to reverse the science score decline but may be hindered in reaching that goal by the fact that Arlington does not require as many science courses as other school systems do.

Scores of eighth grade students also were below those recorded by the same class in the sixth grade. The results were less alarming, however, because all the eighth grade scores put the class above the national standing it achieved in the fourth grade.

Sixth graders increased their math scores over their second and fourth grade levels and pushed reading scores above their national standing in the fourth grade. Fourth graders also improved their relative standing in reading.

Cuban said factors other than the instructional program can play a role in the relative scores of a class as it progresses. Such factors, he said, include variations among tests given in different years and changes in income levels and other characteristics of a class as it moves through a school system.