A new Army intelligence study has increased substantially the estimate of North Korean ground combat power. furnishing new arguments to opponents of President Carter's plan to withdraw U.S. ground troops from the divided peninsula.

The new study, which is the subject of controversy within the government, reportedly concludes that North Korea has the equivalent of about 41 divisions rather than 25 divisions as previously estimated. A major increase in numbers of tanks and other weapons is also reported.

An account of the new study published Tuesday by Army Times prompted a demand by two members of Congress yesterday that Carter halt further U.S. troop withdrawals.

Reps. Samuel S. Stratton (D-N.Y.) and Robin L. Beard (R-Tenn.), chairman and ranking minority member of the investigations subcommittee of the House Armed Services Committee, asked Carter by letter to furnish details of the intelligence data without delay and to stop the pullout until the committee can make a full evaluation. Stratton has been an outspoken critic of the troop withdrawal program.

State Department officials said there has been "no sudden surge" in North Korean military strength, but that the new estimates evidently reflect improved U.S. recording of a gradual increase over a long period of time. Although there is still no agreed estimate within the overall intelligence community on precise numbers. State Department officials said it is agreed that North Korean ground forces are "substantially stronger" than previously believed.

No figure is available on the actual increase in the number of North Korean army troops, which have been reported in the past to be about 440,000. South Korea is reported to have an army of about 560,000 men, organized in larger divisions than those maintained in the North.

The United States has removed about 3,600 of its 40,000 ground troops under Carter's withdrawal program, and is scheduled to withdraw 2,400 more during this year.

Revision of the intelligence estimate on North Korean military strength was reported to have started with a unit of Army intelligence assigned to the National Security Agency. The source of the information raised eyebrows in official circles because the Army stands to lose most in the troop withdrawal plan, and Army commanders in Korea and else-where are reported strongly opposed to the pullout.

The first Army report claiming a major increase in North Korean strength was said to have been made last February on the basis of a large increase in the number of tanks detected by photographic and signal intelligence. A governmentwide intelligence task force was established in May to gather and assess further information.

The analysts have been working "70-hour weeks" on the problem in recent months, according to an official. Army Times reported that analysts have reexamined satallite photo intelligence from the early 1970s to the present as well as agent reports going back to the mid-1960s and signal intelligence data back to the time of the Korean war.

North Korea presents one of the most difficult intelligence problems anywhere to U.S. analysts. Much of the North Korean force is hidden in caves and other inaccessible places, and the North Koreans do not use tactical radios as much as other communist armies. Defectors or agents with access to large amounts of information are rare.

"The intelligence community's revision of the estimates [on North Korea] is an ongoing process to monitor changes," said a State Department official. Some changes in the estimates are made frequently, but such a large change is relatively rare, officials said.

Congressional committees were informed in classified briefings last summer that a major restudy of North Korean military strength was under way, but they were given no details. Congressional requests for additional briefings have been refused on the grounds that the interagency study is not complete.

It is unclear what effect, if any, the Army study or the completed interagency findings will have on Carter's plans to withdraw all U.S. ground combat troops by about 1982. The interagency intelligence report will go to the Joint Chiefs of Staff, who may then restudy their attitude on the troop withdrawal in the light of the additional information.

A State Department official noted that Carter has pledged to take the military situation on the ground into account in deciding how and when to proceed with increments of the troop withdrawal. A law passed last year requires extensive reports to Congress -- including data on the military balance in Korea -- 120 days before the withdrawal of significant numbers of U.S. troops.