Women soldiers are barred from so many career specialties in the Army that their morale has sunk, endangering the volunteer Army, a Pentagon advisory group has told Defense Secretary Caspar W. Weinberger.

He recently received a letter from the group warning of the "serious negative" consequences of the service's effort to limit roles of women soldiers.

The Army recently told more than 1,200 to find new specialties because their current jobs might involve them in combat, and others may soon be reassigned because of the physical requirements of their jobs.

"The closing of military occupations impacts negatively on career development for women, making their advancement difficult if not impossible," wrote Mary Evelyn Blagg Huey, who heads the Defense Advisory Committee on Women in the Services. "In addition to the questionable legality of such direct consequences, this 'domino effect' poses concerns for morale, enlistments and the continued success of the all-volunteer Army."

The actions result from the Reagan administration's decision to reassess the role women should play in the military. Its officials believe that the Carter administration allowed the number of women soldiers to grow too fast and without enough thought about problems they might encounter.

Spokesmen for Weinberger declined to discuss Huey's letter, to which the defense secretary has not replied. But Lawrence J. Korb, assistant secretary for manpower, agreed to talk about the issues it raised and said the administration is not seeking to exclude women from the military.

"The bottom line is, the women we bring in, we want them to succeed," Korb said. "And the number is going up, not as rapidly in terms of percentages, but it is going up."

The number of women on active duty in the Army soared from almost none to more than 150,000 during World War II and then fell back to fewer than 15,000 after the war. During the 1970s, the number climbed steadily to more than 70,000 by 1981, close to 10 percent of the force.

Carter officials projected an increase to 87,000 enlisted women by 1986, a number Korb said "wasn't based on any analysis." The Reagan administration scaled that goal back to 65,000 and last spring eliminated 23 job specialties that the Pentagon decided might involve women in combat.

These specialties included plumbers, electricians and masons.

Huey, who chairs the advisory committee part-time and serves as president of Texas Woman's University, said many of those specialties offer the kind of experience the Army demands for promotions. She said closing them to women has caused "a very serious, widespread effect on morale" throughout the services.

The Air Force and Navy exclude women by law from potential combat positions, which keeps women off submarines and most jet aircraft and ships. The Army has a similar combat-exclusion policy, but it has a harder time defining which jobs might place women in combat.

"The combat exclusion is something we're going to have to live with, whether we like it or not," Huey said in a recent telephone interview. "The question is whether this is the way to make it work."

Army Times newspaper recently has been publishing letters from disgruntled female soldiers suggesting that the military finds room for women when necessary, during wartime or poor recruiting years such as the late 1970s, then excludes them when recruiting improves or the need diminishes.

"There is a popular belief that there is a relationship," Huey said. "I do not know whether there is or not."

Korb said the Army began studying the role of women before recruiting improved. Saying the study was in response to higher female attrition rates and other problems, Korb added, "Women were being put into jobs for which some of them didn't have the physical wherewithal."

Army officials were unable to provide numbers of women who ultimately may be affected by the current reassessment. The advisory committee asked Weinberger to halt further reassignments and to interrupt a similar Marine study.

"As a study reaffirms the positive performance and contribution by those of our gender, a new one seems to be ordered," Huey wrote. "This finally raises the question of whether objectivity or the 'right answers' is the purpose."