The Joint Chiefs of Staff have launched a broad review of the military balance between North and South Korea with an eye to determining whether the planned U.S. troop withdrawals are still an acceptable risk.

Air Force Gen. David C. Jones, chairman of the Joint Chiefs of Staff, said yesterday that the review was triggered in part by new intelligence estimates on the strength of the North Korean military.

Although North Korea appears stronger than originally thought, Jones said the chiefs have not decided yet whether the new estimates and other developments compel a change in the military body's endorsement of President Carter's troop withdrawal plan.

Since Carter's plan calls for withdrawing only 2,400 U.S. troops from South Korea this year, Jones said, the chiefs have time to conduct a thorough study in 1979. The larger withdrawals are scheduled to take place between 1980 and 1982.

Revised Army and Central Intelligence Agency estimates credit North Korea with an army of from 560,000 to 600,000 men, or about one-fourth larger than previously estimated.

"We probably would have conducted the review anyway," said Jones in an interview after making a luncheon address to newly elected members of the House and Senate and their staffs, but the revised intelligence estimates made a new study imperative.

In discussing the new strategic arms limitation treaty (SALT) in the final stage of negotiation, Jones said that while the chiefs will reserve their judgment until the final document is in hand, they will insist on at least these three conditions before endorsing any new agreement.

"That the treaty be fair and equitable and stand on its own merits.

"That we be allowed to work with our allies in Europe to modernize our long-range theater nuclear systems to offset the imbalance created by the Soviet deployment of the SS20" intermediate range, mobile missile.

"That we have the programs necessary to maintain essential equivalence, and overall balance, with the Soviet Union."

In a remark that critics of a new SALT agreement are likely to quote in the future, Jones said yesterday that the "greatest increase" in Soviet military capability "has occurred since the signing of SALT I and we don't see any evidence of slackening effort on their part."

The chiefs have been pressing for a new land missile, the MX, to keep ahead of increasingly accurate Soviet strategic missiles. Gen. Lew Allen Jr., Air Force chief of staff, urged support of that program in a recent letter sent to the House Armed Services Committee.

Hiding each MX missile in a field of identical holes to keep Soviet gunners guessing which hole held the missile "is the most cost effective of all the concepts studied," Allen wrote the committee.

He said the Air Force has devised a way to enable the Soviets to keep track of how many MX missiles the United States deployed without at the same time disclosing which of thousands of holes the missiles were in.

The MX missiles, under the Air Force's scheme, would pass through a choke point in full view of Soviet satellites. The Soviets could count the missiles going through. After passing through the single choke point, the MX missiles would be covertly deployed in missile fields located on government land in several parts of the nation.