Defense Secretary Harold Brown yesterday defended President Carter's veto last month of the defense procurement bill, but in the process may have added to the controversy by identifying new items cut by Congress that he said would "seriously degrade the Army's combat readiness and weaken NATO preparedness."

Similar reductions already mentioned by the president and his Office of Management and Budget have drawn intense criticism from members of Congress who are involved in the defense budget process.

The Brown letter, sent to House speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.). also showed some disagreement between the Pentagon and OMB over just which reductions have cut into "the muscle of our military requests" - the president's description of what congress did.

Brown repeated the administration's contention that $2 billion of high priority defense items had been cut from the Pentagon budget "in order to provide for a $2 billion nuclear powered aircraft carrier."

The chairmen of the House and Senate Armed Services committees have stoutly denied this, and have said the president was mistaken in describing reductions made in both the defense authorization and appropriation bills.

In his letter, Brown listed six items cut from Army procurement requests, a category the president said totaled some $800 million out of $1 billion he had requested.

Leading the Brown list was "loss of 28 needed helicopters."

According to the House appropriations Committee, $100 million was deleted for helicopters the Army plans to leave in South Korea when U.S. troops withdraw. The committee said it had no objection to give Korea the helicopters but wanted the transfer financed out of foreign aid rather than Pentagon funds.

Also on the delection list were 360 armored personnel carriers costing $30 million. Here the Appropriations Committee had approved 550 that were equipped with the TOW antitank gun but held back on the others, saying that without TOWs the Army should wait to procure a different and more modern personnel vehicle.

Brown also listed reductions of 70 M160 tanks and 80 Roland missiles, items totaling some $75 million.

Congress had approved 410 M60s in the bill and had held back on the missiles because, a Senate committee argued, they had not been adequately tested.

The defense secretary's list also included a reduction of $230 million in ammunition stocks, while OMB had identified $353 million in ammunition reductions that were critcal. The $123 million difference results from disagreement over how to analyze Congress did, an administration source said yesterday.

"OMB has its own particular gripes," a Defense official said yesterday in refusing to accept cuts the budget agency had labeled critical.

Overall, however, the Brown letter identified only $577 million of the $800 million in Army procurement Carter said had critically reduced "our ground forces, particularly our NATO-oriented forces."

The remainder of the key items cut, a Defense official said yesterday, "were all kinds of cats and dogs, the list goes on and on." But he added, "I don't want to denigrate their importance."

Pentagon officials are preparing a detailed list of the items they want put back into both the vetoed $37 billion authorization bill and the $126 billion defense appropriations bill that is still before the Senate Appropriations Committee.

Brown's letter yesterday said $457 million in "needed programs" was cut from the authorization bill and $1.6 billion from the appropriations measure that passed the House.

Details of those programs would be presented to the House if the president's veto is sustained next week. Some of that information may be included in a letter to the House Armed Services Committee chairman, Melvin Price (D-Ill.) being drafted in answer to a sharply critical letter he sent Carter Thursday.