''These weren't the Pentagon papers,'' Mr. Nachman said of the 56-question answer key. ''What made the story was not the uniqueness of the documents but their omnipresence.''

The cancellation of the test upset the plans of tens of thousands of students. And the standing of some of them to graduate on time could be thrown into doubt by their inability to take the test. New Test for Chemistry

Commissioner Sobol said a new test for chemistry would be developed and offered to students in August, a move that would cost the state nearly $250,000 and would force local school districts to reopen their schools then and offer new preparation courses.

The first statewide cancellation of Regents exams occurred in 1974, when a scandal involving illegal answer keys led education officials to halt tests in nine subjects. In a few cases since then reports of pilfered answer keys have led to the invalidation of test results in individual schools.

At a news conference here, Mr. Sobol said that while answers to the test appeared to have been ''widely available'' in New York City even before The Post came out today, ''they were not widely available in Syracuse, Rochester, Buffalo, Hogansburg, Lake Placid, Skaneateles and other points north of Fordham Road.''

For that reason, he said, he had not planned to cancel the test statewide until The Post's editions came out early this morning. Instead, he said officials planned to review the test scores in schools or communities where they believed answers had been sold, and possibly take action in individual cases.

Mr. Nachman, the Post editor, said education officials were incorrect in asserting that upstate students had no access to the answers until this morning. ''They're talking as if there were some sort of cordon sanitaire separating upstate from downstate,'' he said. ''It just isn't true.'' Mr. Sobol said he was ''saddened'' that a large number of students appeared willing to cheat. Asked by one reporter what drove the students to such action - ''Is it the pressure put on them, are the courses too tough, is it the difficulty of getting into college?'' the reporter asked - Mr. Sobol answered, ''All of the above.'' A Standardized Measure