The third-ranking U.S. Army general in South Korea says that President Carter's plan to withdraw U.S. troops here in the next four to five years is a mistake that will end in war with North Korea.

"If we withdraw our ground forces on the schedule suggested it will lead to war," said Maj. Gen. John K. Singlaub, chief of staff in the U.S. Forces Korea headquarters.

Singlaub said he and many other senior military officers challenge the wisdom of Carter's plan, and predicted that withdrawal of the war-ready 2d Infantry Division in that time frame would seriously weaken defenses in the South and encourage North Korean Peresident Kim II-sung to attack.

The unusual situation of serving generals, openly differing with the President's declared policy arises on the eve to talk to implement that policy.

Philip C. Habib, under secretary of state for political affairs, and Gen. George Brown, chairman of the Joint Chiefs of Staff, are to arrive in Seoul May 24 as the President's special representatives.

Some military officers, saying the planned withdrawal may jeopardize gains made here over the past 24 years and pose serious military and credibility problems, are trying to influence Washington policy decisions.

"I don't know anybody who is not staggered by it," a headquarters Army officer said of the planned withdrawal "There's no military or strategic logic for withdrawal. In fact, there's a very good case for reinforcing" American strength in South Korea.

Senglaub, a World War II veteran with a distinguished combat record, said he is deeply concerned that decision-makers may be working from outdated intelligence that substantially underestimates current North Korean strength.

"The question asked after U.S. setbacks in China and Vietnam was, 'Did the military people in the know express themselves loudly and clearly enough that the decision-makers understood?' We want to make sure." he added. "If the decision is made we will execute it with enthusiasm and a high level of professional skill."

The apprehensions voiced by Singlaub are enchoed to some degree by many, if not all U.S. military leaders in South Korean. "No one understands why they are being pulled out," said a well-informed American source. "Carter says that withdrawal won't endanger South Korean security or upset the military balance. Out military people say that would be a miracle. They think it can't be done."

The commander-in-chief of United Nations and U.S. forces in South Korea, Gen. John W. Vessey, has expressed his misgivings directly to President Carter and Defense Secretary Harold Brown, source here say.

Singlaub and Vessey's deputy, Lt. Gen. John J. Burns, expressed their concerns in separate lengthy interviews today.

Burns said he would prefer the ground troops to stay.

"The withdrawal must be managed to avoid any disastrous change in the military balance on the Korean Peninsula or credibility of the American commitment. American Air Force Units which Carter has said will stay in Korea should be reinforced," added Bruns, who flew 102 combat missions as a fighter pilot in the Korean War.

Some officers stress the fear that - despite all assurances to the contrary, the drawndown will be interpreted in South and North Korea as a disengagement.

A well-connected U.S. colonel says that South Korean officers who believe that the United States abandoned South Vietnam are asking: "Why are you giving up everything you've accomplished here? They quote the old Korean proverb, 'Don't believe the Americans," he recounted unhappily.

The concern centers around the 14,000-man 2D Division, which has a vital role covering the main southboun invasion route to this capital.

The division's firepower, mobility, ground-surveillance radar and technology give it a far higher combat value than any single South Korean Division. It has more helicopters, and TOW missiles to stop North Korea's 2,000 tanks, than the whole South Korean army. Even if Seoul could afford to buy the advanced weaponry, it would take longer than the scheduled five years to train the South Koreans in its use and maintenance, U.S. officers here say.

The 2d Division is also the controversial "tripwire," which doves argue could lead to U.S. embroilment in another Asian land war and which hawks maintain has successfully deterred aggression since 1953.

Reinforced American air power, which could be flown out a easily as it could be flown in, is not seen as a full replacement for the ground commitment. "Warplanes are like geese," said a U.S. source. "They can honk and fly away. Who really believes that if we don't have the resolve to keep troops in Korea that we're going to bring them back if a war starts?"

"An intensive intelligence effort over the last 12 months has discovered North Korea to be much, much sronger than we thought," Singlaub said. "My deep concern is that people making the decisions are basing them on information that's two or three years old."