White House officials said yesterday that the Pentagon has undertaken a study for President Carter on how many strategic missiles would constitute "minimum deterrence," meaning just enough to persuade the Soviet Union that launching a nuclear attack on the United States would be a losing proposition.

But those same officials denied the assertion in the column by Rowland Evans and Robert Novak, which appeared in The Washington Post and other newspapers yesterday, that Carter had ordered Air Force Gen. George S. Brown, chairman of the Joint Chiefs of Staff, "to plot a Free World defense based on only 200 to 250 submarine-launched missiles."

Carter did not issue any such order to Brown at a meeting with defense leaders at Blair House on Jan. 12. White House officials said, but the President-elect did ask at that session with defense leaders what would constitute minimum deterrence.

He was told, Carter administration aides said, that the United States and the Soviet Union could deter each other from launching a nuclear attack if each side had between 200 and 250 submarine missiles deployed. An outside arms specialist gave roughly the same estimate to Carter earlier, administration officials said.

Given Carter's expressed interest, Brown said he would have the Joint Chiefs conduct fresh studies of minimum deterrence along with other strategic issues, White House officials said.

The strategy of relying on sea-based missiles rather than the more vulnerable land-based ICBMs is known as the "Blue Water Option."

One of the several places it has been advanced in recent years was in the 1971 report by the Members of Congress for Peace Through Law, Vice President Mondale, then a Senator, and Rep. Lucien N. Nedzi (D-Mich.), a ranking member of the House Armed Services Committee, were among those who signed the report.

That report said that submarines with long-range missiles - which is what the Trident submarines under construction are "would be the epitome of the Blue Water option. if our land-based deterrents are so vulnerable and by necessity draw fire close to metropolitan areas, then send the deterrent to sea."

The United States plans to build 11 Trident submarines, each of which would carry 24 Trident missiles with a range of 4,600 miles. Each Trident missile would carry a cluster of H-bombs in its nose, just as the Poseidon missile now at sea carries up to 14 bombs.

One former Pentagon official who had top secret clearances has said that with 10 Trident submarines at sea, each with 24 missiles armed with 10 H-bombs apiece, the United States could launch 2,400 warheads at the Soviet Union with a total blast power of 330 megatons. Right now, the United States and Russia have 8,500 and 4,000 warheads, respectively, targeted on each other.

One Trident missile, with 1.4 megatons in its multiple warhead, would pack 70 times the explosive power of the U.S. atomic bomb dropped on Hiroshima in 1945.

White House and Pentagon officials, after refusing to address the issue when queried Wednesday by The Washington Post about the Evans-Novak column, sought to allay such fears yesterday. Said White House spokesman Jody Powell at the White House news briefing yesterday:

"It is not under active consideration" to reduce the present force of land-based missiles. "Any reduction would have to be accompanied by a mutual and balanced reduction by the Soviet Union . . . Strategic options, from the lowest to the highest, are under continuous review . . . Any implication that we are on the verge" of a big reduction in the U.S. strategic missile force "is incorrect and preposterous."

At the Pentagon, the Post on Wednesday asked Defense Secretary Harold Brown whether the Evans-Novak column was correct in asserting that Secretary Brown at the Jan. 12 meeting had warned Carter that reducing the missile force to 200 to 250 strategic missiles would be a fundamental risk involving the most complex, transcendent questions.

"That is not an accurate quotation of me," Brown replied. He indicated to aides that he was astonished that the discussion that took place had leaked to the press: "That was a small enough meeting - it's very interesting," he said.

But neither Powell nor Thomas B. Ross, Pentagon spokesman, would deny Wednesday when queried the principal assertions in the Evans-Novak column. Instead, the spokesmen limited themselves to a formal statement that, despite protests, amounted to a "no comment."

When he was asked about the Evans-Novak column Wednesday night, Powell, after checking with Carter, replied:

"The President doesn't intend now or in the future to comment on reports of opinions he asks for concerning hypothetical situations. Any reduction in our strategic capabilities would have to be accompanied by a mutual and balanced reduction by the Soviet Union . . . The President will take no action that in any way would impair the national security."

The subject of weapons came up unexpectedly again yesterday at the White House when Carter welcomed a group of junior high school students from West Chester, Pa., to the executive mansion. The President invited questions from the students, and the first one was whether he planned to cut funds for development of the B-1 bomber.

Carter replied that he would not decide on that until the spring, after a through study. He added:

"My own hope as President is to explore every possible way with the Soviet Union and our potential adversaries to cut down the dependence on weapons of all kind. I would like our nation to take the leadership role."