Maria Bruce and most of her civilian and military coworkers were jubilant yesterday as the Army announced it has dropped tentative plans to move its Military Personnel Center from the Hoffman Building in Alexandria to Ft. Benjamin Harrison in Indiana.

"It's great," said Bruce, an Hispanic coordinator at the center who has been one of its 1,660 civilian employes since 1971.

"As far as I was concerned, they were just going to have to move the center without me. I was not going with them," said the Alexandria resident, who was not about to leave her military husband and several members of her family to follow her job to Indianapolis.

The possibility of moving the center and other Defense Department facilities out of the Washington area has been under study since last April, been under study since last April, much to the consterntion of Reps. Herbert E. Harris (D-Va.), Gladys Noon Spellman (D-Md.) and other Northern Virginia and Maryland lawmakers.

The argument that apparently scuttled the Alexandria move at the Pentagon, according to an Army letter sent yesterday to members of Congress, was the study's conclusion that the move from Washington would be too expensive and inconvenient.

"Relocating the center would not be cost effective and . . . anticipated losses of civilian employees who would not elect to move would adversely affect the center's ability to perform its mission," said the letter released by Harris' office.

The Army thus assured Harris and others that the center would remain at its present location and "all of these jobs would remain in Alexandria." In addition to the civilian jobs, another 896 of the center's work force is military.

Alexandria's retention of the Military Personnel Center, which keeps the records and monitors the training and career progress of 740,000 Army personnel, was a noteworthy survivor amid the Defense Department's announcement of several military base closings, transfers and economy realignments in Virginia and around the nation.

"The pressure was really on to save this one," said Rep. Harris about the Alexandria facility. "They were talking about a large number of transfers over a long distance, and we tried to get them to crank in the cost of losing these experienced people who would not move."

Harris said that he hoped maintaining the status quo on the Military Personnel Center would discourage what he said has become "political poaching on the Washington area" as lawmakers from other states try to pressure the military into relocating in their districts.

In addition in a favorable decision on the Alexandria center, the Army announced that the Harry Diamond Laboratories in Woodbridge-location of the U.S. Army Intelligence and Service Command-will get an extra 189 civilia and 55 military positions resulting from transfers from Arlington Hall in Arlington and Vint Hill Farms in Fauquier County.

Also, the Army said the Naval Hospital at the Quantico Marine Base will be closed to be replaced by a Naval regional medical clinic providing out patient services.

The hospital's closing will affect 36 out of 60 civilian employes, most of whom the Army said it will reassign. By treating military patients and their dependants at nearby hospitals, the Army hopes to save $2 million a year.

Also slated for closing, sometime in 1982 or 1983, is historic Fort Monroe in Hampton, Va., a 156-year-old military complex whose construction was supervised by a young U.S. Army officer named Robert E. Lee.

The fort's 2,092 civilian and military personnel will be shifted to other posts, and the Army has promised to make every effort to find jobs at nearby facilities for the 868 civilian employes affected by the closing.

At the Hoffman Building, however, workers in the twin tower high-rise at 200 Stovall St. near the Beltway were relieved to know they will not have to go job hunting.

"I'm married and my husband works here and it's been my home for many years," said Helen Arensforf, a supervisor in the center's word processing unit. She is among the 70 percent female work force at the center, many of whom have family ties to the area that would have prevented them from making the move to Ft. Benjamin Harrison.