President Carter said yesterday that reports that the administration plans a $2 billion expansion of civil defense programs "have been completely erroneous" and that no such proposal has ever been made to him.

At a nationally televised news conference, Carter appeared irritated over press reports of a $2 billion civil defense program and suggested by his tone that he would be skeptical of such a large undertaking.

"I have never been able to find where the origin of that story might have derived," he said. "No proposal has ever been made to me for a civil defense program of that magnitude."

Administration officials said later that the projected five-year cost of a White House-approved policy to improve the capability to evacuate major metropolitan areas in case of a nuclear crisis is $1.3 billion, including inflation.

The Pentagon has recommended that, to begin the relocation program, civil defense spending for the fiscal year that begins Oct. 1 be increased by about $45 million, to $145 million. But officials stressed that neither that proposal, nor the longer-range projections of costs, have reached the president and could be changed.

Carter, with the strong support of national security affairs adviser Zbigniew Brzezinski and Defense Secretary Harold Brown, last September approved launching the "crisis relocation program" but did not set specific goals for it.

According to White House officials, Brown then ordered a study of providing the nation with the capability to evacuate major metropolitan centers during a one-to-two-week period. Out of that study the projected five-year cost, variously reported at $1 billion to $2 billion, emerged, the official said.

Bardyl R. Tirana, director of the Defense Civil Preparedness Agency, confirmed last night that Carter has made no spending decisions on expansion of civil defense programs.

Tirana said a number of projected figures have been used, depending on "how much you want to buy." In congressional testimony last spring, he said, he estimated a cost of $230 million a year over a five-year period.

Tirana said he has not seen a $2 billion figure used as part of official government projections.

The president's decision to approve an enhancement of U.S. ability to evacuate its cities in a time of nuclear confrontation has been widely interpreted as being part of a deliberate strategy to soften criticism of a new strategic arms limitation treaty (SALT) agreement with the Soviet Union. This and other steps to beef up defense spending are seen, in part, as efforts to answer critics who charge a new SALT accord would give the Soviets nuclear superiority.

Carter, however, denied yesterday that an enlarged civil defense program was part of an overall strategy to win Senate approval of a SALT agreement.

He also said that he has made no decisions on spending next year for two major new weapons systems -- the MX "mobile missile" and the Trident submarine.

"We are considering the advisaiblity of pursuing some civil defense assessments, including the fairly long-term evacuation of some of our major cities if we should think that nuclear war would be likely...," he said. "But I have not yet decided to move on the MX or, if to move on the MX, what to do about making sure that our present silo missiles are secure."