The Pentagon yesterday called off a high-level invasion of the Democratic National Convention.

As of noon, the plan called for Defense Secretary Harold Brown, Army Secretary Clifford L. Alexander, Navy Secretary Edward Hidalgo and Air Force Undersecretary Antonia H. Chayes to go to New York next week for the convention.

Pentagon spokesman Thomas B. Ross, in confirming to the Washington Post that the defense executives planned to attend, had said the unusually large Pentagon delegation would be available for media interview during their stay in New York.

GOP nominee Ronald Reagan has made President Carter's defense policies a central issue in his campaign. Ross said "a whole range" of defense issues was likely to come up during next week's convention. A number will be debated in the fight over the platform.

While denying any intent to politicize the Pentagon by having its executives attend the convention, Ross had added, "We're not going to miss any opportunities to respond to erroneous charges.

Before coming to the Pentagon, Alexander, a black, served as special consultant to President Johnson on civil rights; Hidalgo, a native of Mexico, was active in Hispanic causes, and Chayes, the first woman to become undersecretary of the Air Force, was a political activist.

These backgrounds would have been a political dividend for Carter at the convention.

However, after The Post pressed the Pentagon executives to explain their role at the convention, Defense Secretary Brown had second thoughts about letting them attend.

Ross called The Post late yesterday to say that none of the four Pentagon executives, except possibly Brown, would attend the convention after all.

"On reflection," Ross said, Brown decided that the attendance by Alexander, Hidalgo and Chayes might look like a departure from the practice of keeping the Pentagon "outside of polictics."

But Brown's change of heart took some time to get to the other would-be attendees. The Navy said Hidalgo was going on leave all next week so he could attend the covention from Monday on -- a statement Brown made inoperative.