Defending his plan to withdraw American ground troops from South Korea, President Carter said yesterday that Maj. Gen. John K. Singlaub committed "a very serious breach" of the military command system by publicly asserting that the withdrawal will lead to war.

The President, who abruptly ordered Singlaub removed as the chief of staff of the American military command in Korea, said the general's remarks might encourage North Korea to invade the South and amounted to "an invitation to the world to expect an inevitable war.

"And I certainly don't agree that there is any cause for a war to be expected," he added.

Carter also insisted that in removing Singlaub from the No. 3 military post in Korea he had not "fired" the much-decorated war hero, nor had Singlaub been "chastised or punished" for speaking out.

"He was being transferred to a new position at an equivalent degree of responsibility and stature," the President said. Singlaub's new assignment has not been announced.

Carter spoke during a nationally televised news conference amid other developments in the Singlaub affair, which has focused attention on the president's pledge, first voiced during his campaign, to withdraw U.S. ground troops from Korea over a four-to five-year period.

In Seoul, at the end of two days of talks with American officials about the withdrawal policy, a top aide to South Korean President Park Chung Hee suggested that South Korea might push for the development of its own nuclear weapons if the United States removes its tactical nuclear weapons as well as troops from the country.

"As a matter of principle we should have the freedom to take necessary actions within our ability to ensure our own survival," the Park aide said. "As to the question of nuclear weapons development, we would consider ( See KOREA, A6. Col. 3 ) ( KOREA, From A1 ) the matter on that basis." He did not elaborate.

At the Pentagon, spokesman Thomas B. Ross said the Joint Chiefs of Staff were "competely involved" in developing the withdrawal plan and had posed no objections to it.

On Wednesday, Singlaub had told a House Armed Service subcommittee that the chiefs had given no rationale for the withdrawal to the American military command in Seoul.

Singlaub had been called to testify before the subcommittee in what administration supporters described as a "frontal assault" on Carter's policy in Korea.

Meanwhile, House Armed Services Committee Chairman Melvin Price (D-III.) said the full committee will take over from its investigations subcommittee the examination of the whithdrawal policy because of the "importance" of the issue.

Shortly after Congress returns from its Memorial Day recess on June 6, the full committee is expected to call the Joint Chiefs of Staff to give their personal opinions of the withdrawal plan.

Ross said Pentagon officials had no objections to the military chiefs testifying on the plan.

Any attempt by South Korea to develop its own nuclear weapons would run head-on into the President's strong stance against the spread of nuclear materials around the world. Carter said during his campaign that U.S. nuclear weapons should be withdrawn from Korea, but he has not repeated that statement as President.

According to news reports, some nuclear weapons have already been removed from Korea, but others remain.

South Korea is a signatory to the nuclear nonproliferation treaty and government officials have repeatedly said there is no plan to develop nuclear arms. The United States has strongly opposed any Sounth Korean nuclear capability and several years ago exerted heavy pressure on Seoul to cancel plans to purchase a nuclear reprocessing plant from which nuclear weapons could have been fashioned.

Singlaub ignited the review of Korea policy in an interview, published May 19 in The Washington Post, in which he called the withdrawal plan a mistake that "will lead to war," He said, both in the interview and in his congressional testimony, that his misgivings are widely shared among American military officials in Korea.

The same day the interview was published Carter ordered Singlaub to return to Washington. Two days later, at a face-to-face meeting at the White House, the President removed the general from his Korean command.

In defending his decision yesterday, Carter cited support from such diverse sources as South Korean President Park Chung Hee and former Republican Defense Secretary Melvin Laird, both of whom, he said, had advocated the complete withdrawal of U.S. ground troops from Korea.

"There has never been a policy of our government evolved for permanent placement of ground troops in South Korea," he said.

"There essence of the question is, is our country committed on a permanent basis to keep troops in South Korea even if they are not needed to maintain the stability of that peninsula?" he continued.

"I think it is accurate to say that the time has come for a very careful, very orderly withdrawal over a period of four or five years of ground troops, leaving intact an adequate degree of strength in the Republic of Korea to withstand any foreseeable attack and making it clear . . . that our commitment to South Korea is undeviating and is staunch."

Among American forces that would remain in Korea under his plan, the President said, are intelligence, Air Force and Navy units.

He said that the factors behind his decision included a confidence in the ability of South Korea to defend itself and a recognition that the relationships among the major powers in the area - the United States, Soviet Union and China - have changed in the 25 years since the Korean War.

Carter dismissed one questiner's suggestion that he had employed a "double standard," discipling Singlaub while tolerating public remarks by U.N. Ambassador Andrew Young that appear to be at odds with administrationpolicy.

"I know of no instance that Andy Young has violated a policy . . .," he said.

The President said Singlaub was removed from his post not only because of "a very serious breach of the propriety that ought to exist among military officers after a policy has been made" but because his effectiveness in Korea had been seriously damaged.

"I don't believe that Gen. Singlaub, being our negotiator with the North Koreans, by the way . . . could have effectively carried out this policy when he had been identified as being opposed to it," Carter said.

He added that Singlaub's continued presence in South Korea would have been "a disturbing factor," attracting "admiration and attention" from others opposed to the withdrawal policy andhampering efforts to acarry it out.