The Army is seeking to reverse the Pentagon's current policy of allowing servicewomen to decide for themselves whether to remain in the military after becoming pregnant.

Lt. Col. Robert N. Waggoner, an Army personnel officer, said yesterday that Army commanders want to make that decision on the basis of what is best for the service.

"The issue is one of managing the force," Waggoner said in a speech before the Defense Advisory Committee on Women in the Services.

The Army's request for regaining authority over the futures of pregnant women in its ranks has hit a stone wall in the Defense Secretary's office. Neither former Defense Secretary Donald H. Rumsfeld nor Secretary Harold Brown has acted on requests for a return to the old policy. Army officials said they do not expect an approval any time soon, either, because of the protests that would be generated.

Waggoner said there is a lot of emotionalism surrounding the pregnancy question, adding that "we know that's not absolutely correct" to consider women "the bad people" when pregnancy occurs.

He said Army commanders, if they did regain the authority to decide whether pregnant women should remain in the service, would act reasonably. With that decision entirely in the hands of the women themselves, he complained, "there are no inhibitors out there now."

Martin Binkin, Brookings Institution researcher who has just completed a study on women in the military, told the members of the Pentagon's women's advisory committee that the liberalization of defense policy on pregnancy arrived too fast.

Having children and then remaining on active duty under the liberalized policy is adding significant costs to the Pentagon budget, Binkin said.

In discussing how many women the military services could use successfully, Binkin said his study has indicated the services have room for 600,000 women but only plan to accept 126,000 in fiscal 1982.