The chairman of the House government information and individual rights subcommittee yesterday assailed a proposed presidential decree setting up new security classification rules as "a blank check" that could be used to sanction an unprecedented increase in government secrecy.

Rep. Glenn English (D-Okla.) said at the outset of hearings to which the administration refused to send witnesses that he was persuaded the proposal had been made "deliberately vague" so government classifiers could begin slapping a secrecy label on virtually anything they want.

A representative of the American Historical Association said the new mood reflected in the draft executive order, now under consideration at the White House, has already had a chilling effect on the declassification of FBI documents going back to World War II.

Anna Nelson, a George Washington University history professor, said the FBI had been steadily releasing its wartime records on Nazi operations in Latin America and withholding little under the current rules, issued by President Carter in 1978.

"Recently, however, the FBI has become unwilling to go into the National Archives and declassify the rest of those documents," she told the subcommittee.

"No doubt this pattern will be repeated throughout the government as those who read the documents of 10, 20 and 30 years ago bear in mind the new yardstick: when in doubt, classify," Nelson testified.

The proposed new order prescribes a new approach to the stamping of government documents as "Top Secret," "Secret" and "Confidential" and that is, as Nelson said, when in doubt, classify. Even worse from the historians' point of view, Nelson said, is the elimination of the current rule providing for automatic declassification review of records as they become 20 years old.

This, she protested, will "turn back the clock" some three decades to the policies prevailing before President Eisenhower began trying to reform the system and do something about "the massive accumulation of classified information" in government files.

A spokesman for the Society of Professional Journalists, CBS News correspondent Bob Schieffer, voiced his alarm at another provision in the draft order, calling for the classification of information concerning "the vulnerabilities or capabilities of systems . . . relating to the national security."

Schieffer said that blanket could easily have been used to hide the shortcomings of weapons such as the expensive new M1 tank which, because it lacks a digging blade, is going to need a $1 million bulldozer to go along with it.

"I fear that anything open to criticism--any vulnerability--in a proposed new plane or tank or bullet would be shielded from scrutiny under the new order and that our ability to learn how well our money is being spent to arm America would virtually cease," Schieffer declared.

Still other witnesses, such as Morton Halperin of the Center for National Security Studies, complained that the draft order also will broaden greatly the presumption of secrecy for intelligence sources and methods, ostensibly to soothe apprehensions of foreign intelligence services such as Britain's MI6.

In response to complaints from Rep. Thomas N. Kindness (R-Ohio) about the one-sided nature of the hearings, English said he would keep the record open for a week and meanwhile dispatch a letter to President Reagan asking him to reconsider the administration's decision to send no witnesses.