After a year-long study of 400 coastal areas and months of intense lobbying, the Interior Department yesterday unveiled maps that could mean the loss of millions of dollars worth of development for tracts along the Atlantic and Gulf coasts.

Interior's maps pinpointed 188 areas in 16 states that should be defined as undeveloped coastal barriers. Last year's budget reconciliation act specified that those areas be denied federal flood insurance for new construction or significant improvements and left it up to Interior to draw the maps.

Over half of the 747.6 miles designated by the department is in Florida, Texas and Louisiana. Closer to home, the list includes portions of Assawoman Island, Cedar Island, Little Cobb Island and Fisherman's Island in Virginia and Cape May and Stone Harbor Point in New Jersey.

Interior will accept comments until Nov. 15 on the proposal, and then will issue its final list. Coastal barriers on the final list will be unable to get new federal flood insurance after Oct. 1, 1983.

"This provision does not prohibit a property owner from building on his property after that time. It simply advances" the approach that the risk of development in these areas "should be borne by the private sector not underwritten by the federal taxpayer," Ric Davidge, an Interior official who chaired the task force that worked on the policy, said at a news conference.

Coastal barriers are composed of sand or other shifting materials, sometimes making them unsuitable for development. They provide the mainland's first line of defense from hurricanes and other ocean storms. Although commonly referred to as "barrier islands," the list includes land connected to the mainland.

Florida, Texas, North Carolina and South Carolina stand to lose the most under the Interior list because a major portion of the designated land is suitable for development, property values are high and development pressure is great, according to Interior.

Interior expects the impact to be minimal for the New England states, New York, New Jersey, Georgia and Louisiana, where local and state regulations are already strict or where most of the barrier islands on the list are unsuitable for development anyway.

Under current law, Interior cannot put wildlife preserves or other land held by private conservation groups or state and local governments on the undeveloped barrier island list. Interior yesterday asked Congress to amend the law to allow the federal government to deny flood insurance to those areas as well.

Congress is already in the midst of considering legislation that would cut federal funds to these areas even more, by prohibiting the use of funds for such things as highways, bridges and sewage treatment facilities.

Interior estimates that the federal government would have spent between $5.5 billion and $11 billion on undeveloped coastal barriers over the next 20 years, if federal policy had not changed. But opponents of the plan say it could cost developers and builders an equal amount in lost opportunities. Thane Young, director of environmental and energy affairs for the National Association of Realtors, said many builders cannot get financing for construction without federal flood insurance. Davidge suggested that private insurance companies might move in to fill the void, but Young disagreed.