As a former Cabinet member, I vigorously disagree with Thomas K. Turnage's rationale {op-ed, Dec. 23} for elevating the Veterans Administration to Cabinet level. Things sure look different from the inside. When one sits in Cabinet meetings as I have, discussing governmental issues with all departments and the president present, one can truly appreciate the importance of that body as a policy-building tool. But I can also appreciate how its effectiveness is diluted when there is too much discussing and too little deciding.

When the Reagan team took office, the emphasis was on the Cabinet Council system. Its purpose was to go through various policy options and come up with key recommendations for the president to consider. The Cabinet Council becomes more than a forum. It is one of the president's principal ways to forge policy.

My chief concern with the proposal for a Department of Veterans Affairs is that it will reduce the Cabinet's effectiveness. Too many advocates in the Cabinet Room advising the president confuse the issues and are counterproductive. The consequence of a bulging Cabinet will be that it will ultimately force the president to rely more and more on White House staff in private meetings and less and less on his Cabinet in its meetings.

The Cabinet, through sheer size, can be self-defeating if it slows procedures down. Extra Cabinet departments do that. In fact, a case can be made that there are too many secretaries sitting around the Cabinet Room as it is.

President Carter created the Department of Education to reward a particular political constituency. Now we have an effort to recognize veterans with their own department. Turnage tries to make the case that veterans' voices should be heard at the highest level of government.

I disagree with his basic assumption that veterans are not heard now. First, almost without exception, Cabinets are dominated by veterans themselves. As individuals, these Cabinet members are sensitized through their own experiences. I am a West Point graduate, served as an airborne ranger and am a member of the American Legion. As such, I believe in a strong military and support all veterans' organizations. My background is similar to others in the Cabinet. I've been in countless Cabinet meetings, and never once did I get the impression that veterans were being given the short end of the stick. Veterans always got their due.

Second, the VA was set up to meet veterans' needs. Any perceived shortcomings are attributable to factors other than an inability to get the president's ear at a Cabinet meeting. Yes, the Veterans Administration does a great number of things in health, housing and education. But is that reason enough for creating a new department? By that rationale, we'd create a Department of Aging to pull together all the government programs for the elderly. And why not a Rural Development Department?

Organizational consolidation for its own sake is not sufficient justification for another Cabinet office. Veterans have certainly "earned every benefit they receive," but that's not a valid rationale either. Veterans do have a voice as individuals in the Cabinet and as an institutional voice in the VA. We veterans do not need a Cabinet department to look after our interests.

The writer was secretary of Agriculture from 1981 through 1986. He is now president of the National-American Wholesale Grocers Association.