The Army yesterday officially lowered its recruitment goals for women and closed off 23 job categories that they previously had been allowed to fill.

But Reagan administration officials maintained that they were committed to increasing the number of women in the military and that the changes will help women in the military by assigning them to jobs for which they are better suited.

As part of that effort, officials said they would be administering physical strength tests to both men and women, probably at the conclusion of basic training, to determine which jobs the soldiers can perform.

The announcement marked the completion of a 15-month Army study of the role of the women in the military, the first since the Carter administration set ambitious recruitment goals for women and opened up all but 38 of the Army's 354 job categories to women.

Pentagon officials said yesterday that over the next five years they would increase the number of enlisted women in the Army by 5,000, bringing it to 70,000. The Carter administration had set a 1986 recruitment goal of 87,500 enlisted women. One month after President Reagan took office, the Army imposed a cap on female recruitment, holding it at 65,000.

Lawrence J. Korb, assistant secretary of defense for manpower, reserve affairs and logistics, said the changes reflect an "increased role for women in the Army." He said the Carter figures were "based upon no rationale" and were "merely for planning purposes," and thus should not be used for comparison.

Korb said that in closing more job categories to women the administration was merely reflecting the mood of Congress and the public by keeping women out of combat-related jobs. Women have always been barred from combat jobs, and Korb said that until the study was made the Army had not realized that the jobs were combat-related.

He said that about 1,400 women are assigned to the 23 job categories that will be off-limits to female soldiers. But he said those women will not be moved to safer jobs because that would violate the Army's commitment to them.

Most of those jobs are in the engineering field, such as heavy equipment operations, which require both strength and deployment close to battle zones. But the list also includes carpentry and masonry specialists, plumbers and interior electricians.

Mary Elena Torralva, chairman of the Defense Advisory Committee on Women in the Services, which advises the Pentagon on women's issues, said she was pleased that the Army had decided to begin recruiting women again. She said she did not think the physical tests would be unfair to women because the Pentagon had assured her that women who could perform heavy lifting would not be denied strenuous jobs.

Korb said the physical strength tests will be used to determine if both men and women are qualified for jobs that require "upper body strength." He did not elaborate, but he said the Army study has provided the Pentagon with a "blueprint to assure that all soldiers, male and female, will be assigned jobs they can handle."

It apparently does that by classifying all of the Army's jobs according to physical demands. For example, jobs that involve computer programming are considered light work, while engineering jobs are listed as "very heavy work," Korb said. The physical tests will allow the Army to direct soldiers to the "most appropriate" job for them, Korb explained, and will allow the Army to "do more intelligent planning."

Korb said the study's recommendations will "do away with a lot of the frustration and poor performances" that has caused the attrition rate for Army women to be about 14 percent higher than for men. Korb said the departures jeopardize unit cohesion and military readiness.

He said the study, which will not be made public until September because the Army is "still dotting a few i's and crossing a few t's," discovered that less than 10 percent of the women it tested could lift more than 96 pounds. Yet, he said, nearly 64 percent of the Army's jobs require soldiers to occasionally lift more than 100 pounds and frequently lift 50 pounds.

The study also found that 42 percent of the soldiers now in jobs that require "very heavy lifting" (more than 100 pounds) are women.

Korb said further details about the report will be made public at a briefing Monday.