Symptomatic of turbulence within the nation's senior officer corps, the chief of air defense has been relieved of his command for "medical" reasons after writing his superior a stinging private letter charging that a proposed reorganization undercuts U.S. security and sounds the wrong signal to the world.

Gen. Daniel (Chappie) James Jr., commander of the U.S.-Canadian North American Defense Command (NORAD) and the U.S. Aerospace Defense Command (ADCOM), suffered a heart attack in September (medically described as a "cardiac incident"). He was expected to stay in command until retiring six months from now. But that was before his Oct. 20 letter to Gen. David Jones, Air Force Chief of Staff. Both Jones and James deny to us that the letter was connected with James's relief from command, but scarcely any Air Force officer believes that.

James, 57, the first black ever to achieve four-star rank, is noted for moderation and discretion. Hence, the language in his protest to Jones is exceptional. Opposing a Jones-backed reorganization that eliminates ADCOM to save costs, James called the proposal "inaccurate," "superficial" and "biased" and declared that "a perceived de-emphasis in U.S. air-defense priority could signal the wrong intention to both our enemies and our allies."

Typifying discontent among the uniformed military, James's complaint transcends petty bureaucratic grievance and goes to central issues of national survival: withdrawing troops from Korea, junking the B-1 bomber, proposing concessions in strategic-arms and European-force negotiations. These have generated a barely suppressed anxiety at the Pentagon.

The Air Force study heightens this anxiety by proposing that ADCOM be eliminated - its interceptor functions going to the Tactical Air Command, its space-surveillance functions assumed by the Strategic Air Command. To Air Force officers, this climaxes years of downgrading air defense, making the United States vulnerable to air attack.

That this proposal could doom the 30-year U.S.-Canadian partnership in NORAD was disclosed in an Oct. 14 "eyes only" memorandum sent to Ottawa by Canadian Maj. Gen. K. C. Lett, NORAD's director of operations. Contending the Air Force study breaks the U.S.-Canadian agreement, Lett said: "It is underhanded, devious, full of half-truths."

On Oct. 18, the Air Force sent a confidential memo to Defense Secretary Harold Brown summarizing the study. Arguing against a separate Air Defense Command, the summary contends ADCOM could be eliminated "without disturbing . . . our international agreements with the Canadians regarding NORAD." That raised some Air Force eyebrows, considering Gen. Lett's attitude.

About that time, Gen. James, convalescing at home in Colorado Springs, Colo., dictated an eight page letter to Chief of Staff Jones. It was then expected James would reassume his command around Dec. 3. So, according to fellow officers, James knew he was making a bet-your-job gamble in writing Jones.

"I have strong objections to the approach, logic, appropriateness, rationale, adequacy and accuracy of the study," James began. Then he got to the substances. Contending the reorganization would provide only "minimal savings," he said: "If national security is a valid priority, a strong air-defense organization is required." He called perceived de-emphasis in air defense "untimely," coinciding with the canceled B-1 and the coming Soviet Backfire bomber.

Warning the plan would help Canadians who want to withdraw from NORAD anyway, James declared: "I am convinced that the Canadians will not tolerate any significant dependence on SAC for attack warning" (a conviction, confirmed by Lett's memo).

James did not weasel: "The study itself is seriously inaccurate. It is a superficial and biased collection of perceptions about the most serious operational role assigned to United States Forces - 'Are we or are we not under attack?' There is no room for misinterpretation, confusion or mistake."

Shortly thereafter, James was reassigned to Washington. Jones told us the change had "nothing to do with James's letter. James used nearly identical language over the telephone from Colorado: "It has absolutely nothing to do with it. I am going out because of health."

But Chappie James is no shouter and never intended his letter to see the light of the day. Besides, fellow officers say he does not want to agitate black airmen. However, for the officer corps, his departure discloses what happens to a senior officer who protests, even privately, that cost savings undermine security.