ABERDEEN PROVING GROUND, MD. -- Tons of aging weapons now stored in Harford County could be shipped to an atoll 750 miles off Hawaii in the South Pacific, according to a new report under consideration by Army officials.

In addition to offering that option for disposal of the lethal nerve and blister agents, the consultants told the Army they found serious shortcomings in existing plans to evacuate area residents in case of an accident with the potentially fatal mustard agent stored here.

Traffic backups would stall evacuation and there would not be enough time to get people out under current plans, the consultants said.

In addition, the report said, there is no warning system for civilians.

The consultants said it would be feasible to transport Aberdeen's share of the nation's stockpile of chemical weapons by ship down the Chesapeake Bay to the Atlantic Ocean and around South America, with eventual disposal at an incinerator on Johnston Atoll, an island 750 miles southwest of Hawaii.

The Army, which ruled out the possibility of such a move in a July 1986 report in favor of on-site incineration, now says it will consider putting Aberdeen's share of the stockpile on a ship specially designed to transport the one-ton bulk containers of mustard agent as recommended by the consultants, said spokeswoman Marilyn J. Tischbin.

The option of shipping the mustard agent from Aberdeen is part of a report by EA Engineering, Science and Technology Inc., consultants with offices in Hunt Valley hired by the Army last year to address concerns of residents who live near the proving ground.

If the Army continues to recommend on-site incineration at Aberdeen, the consultants urged moving the incinerator 3.5 miles from its currently proposed site, thus narrowing the number of people who could be affected by an accident. That number is conservatively put at about 45,000 in the event, called unlikely, of a serious accident.

Aberdeen houses about 5 percent of the nation's total lethal nerve and blister agent stockpile.

Other disposal alternatives that have not yet been ruled out are construction of two regional incineration sites, at Anniston Army Depot, Ala., and Tooele Army Depot, Utah, and construction of one national incineration site at Tooele.

However, the idea of taking the lethal nerve agents by rail through more than 20 states to those regional or national disposal sites has caused political leaders in those states to balk.

EA ruled out the possibility of airlifting the mustard agent out of Aberdeen.

In addition to Aberdeen, Tooele and Anniston, other sites where the nerve agents are stored are Lexington-Blue Grass Army Depot, Ky.; Newport Army Ammunition Plant, Ind.; Pine Bluff Arsenal, Ark.; Pueblo Army Depot, Colo.; and Umatilla Army Depot, Ore.