Defense Secretary Caspar Weinberger is asking Congress for an additional $30 billion to spend next year, and the chances are excellent that he'll get ti. Yet this enormous spending increase may not be necessary. If "Cap and Knife" would only exercise his demonstrated skills for cutting out waste and fraud, he would find that billions of dollars could be salvaged.

Indeed, one private watchdog group, the Committee on National Security, has compiled a list of Pentagon extravagances. The amount squandered by the brass hats totaled some $32 billion -- enough to absorb Weinberger's entire budget increase, with enough left over for a few F15s and nuclear submarines.

This committee is a group of conservative businessmen and distinguished citizens who recognize the need for a strong defense establishment -- but who abhor the way the Pentagon throws its billions around.

The committee's list of boondoggles that never would be missed was compiled from studies conducted by the Republican Study Committee, the House Appropriations Committee and the General Accounting Office. My associate Indy Badhwar has reviewed the list, and found examples of almost unbelievable extravagance by our military spendthrifts. Here are just a few:

Improving the maintenance and support system for the Navy's FA18 squadrons would save an estimated $4 billion.

Requiring the Air Force to make do with one instead of two computer systems to handle routine administrative functions at each of 105 air bases would save another $1 billion.

Eliminating fraud and faulty accounting in a single Army facility -- the Finance and Accounting Office of the Military District of Washington, D.C. -- would save $531 million.

Standardizing ground service equipment for all military aircraft would save $300 million.

Improved handling of the Navy's shipbuilding contracts could have saved $774 million in the 12-month period studied.

Better inventory control at just two Air Force logistics centers would have saved $50 million.

Proper accounting procedures on the value of foreign military sales: $420 million.

In private business, a standard of competence is furnished by the profit factor. If business branch is wasteful, it loses money or its profits decline, a bell goes off at headquarters, and that branch is either pruned or cut off.

But the Pentagon, with no such automatic arbiter, can always claim that a poor result could be improved with a bigger staff and more money. The brass hat is rewarded, not for efficiency, but by the number of people he has under him -- the more bodies, the higher his rank. Then when someone blows the whistle on military waste, the generals and admirals are inclined to wrap themselves in the flag and proclaim that any criticism is unpatriotic.

President Reagan could do worse than listen to the advice of an old pro, who was the Navy's procurement chief during the Nixon era. He is Gordon Rule, who chewed up Navy budgets and spit out the waste until President Nixon was pressured to put him on a short leash and finally to consign him to the doghouse.

Rule has written to Weinberger about a number of cost-cutting suggestions. Just two of them are enough to send chills down the backs at the Pentagon.

Rule recommended that all Pentagon officials be required to give their congressional testimony under oath -- including their budget estimates and production requirements. This would make the officials liable for prosecution if they deliberately lied about what they needed and how much it would cost.

Rule would also have civilian inspectors general named for each branch of the armed forces to serve as channels for whistleblowers -- with the authority to take action against waste and mismanagement.

The prevailing mood in the Pentagon, meanwhile, is that it is almost subversive not to want to spend more money.