The nation's long-debated memorial to President Franklin Delano Roosevelt, authorized but not yet funded by Congress, would wipe out 8.8 acres of heavily used playing fields in West Potomac Park and erase the much-traveled drive beside the Tidal Basin cherry trees, according to an official assessment of its environmental impact.

The memorial would also, the report says, increase auto traffic in the park by 30 percent, compress it by transforming a present one-way loop around the park into a two-way road doubling back upon itself, and complicate parking for the teams and individuals who pack the park on weekends.

"It is the opinion of the National Park Service that this is not an adverse impact" on the park, the final environmental impact statement (EIS) on the project says. The EIS was released jointly by the FDR Memorial Commission and the National Capital Parks region of the National Park Service.

The 168-page statement, dated in June but only recently distributed, suggests on the one hand that life in West Potomac Park would probably be simpler--and probably better for its present users--were the $31 million monument to the nation's 32nd president never built.

"On the other hand," the statement says, "a no-build alternative would be contrary to a 30-year commitment by Congress to memorialize FDR . . . and would result in the loss of a great potential city and national resource."

The debate over where and how to memorialize the father of the New Deal has been under way ever since his death in 1945. Legislation in 1959 reserved a site for the memorial in West Potomac Park. The FDR Memorial Commission, created by Congress in 1955, has endured stormy debates and public rejection of previous memorial designs, the most famous of which called for giant granite tablets derided as "instant Stonehenge."

The project described in the EIS was approved by Congress in 1982. It would be a slightly scaled-down version of the $46 million to $50 million design authorized by Congress and approved by the Fine Arts Commission in 1978, only to be rejected by the Department of the Interior the following year as too costly.

It would bisect the park's present open fields with 14-foot-high earthen berms and create a1,000-foot-long granite wall, 12 to 14 feet high, meandering around the western edge of the Tidal Basin among waterfalls, sculpture and fountains. It would take five years to build.

Designed by San Francisco landscape architect Lawrence Halprin, the memorial as originally conceived would have been the largest and most expensive one ever built in the United States and would have also been the most expensive to maintain. It would have required an annual operating budget of between $1.2 million and $1.6 million, including a permanent staff of 45 to 49 and a part-time staff of 24--roughly twice the funds and staff needed for the Lincoln and Jefferson memorials. The current plan eliminates a previously proposed interpretive center, tourmobile access road and information kiosk, and shrinks the overall size of the project from 10 to 8.8 acres.

"The 66-acre section of West Potomac Park that Congress designated as the site of the FDR Memorial presently contains a polo field, a rugby field, two cricket pitches, three soccer fields and 11 softball fields," the EIS says.

"Construction of the memorial will require relocation or reorientation of most of these fields."

The EIS states repeatedly that "there will be no decrease in the number of sports fields in West Potomac Park as a result of construction of the FDR Memorial," but adds, "Some sports fields will, however, be relocated."

The principal relocation site, however, will be the area south of the reflecting pool, which the EIS describes only as "formerly utilized by the Smithsonian Folklife Festival." What would happen to the hordes of touch football players, softballers and soccer teams who already fill those fields every weekend the EIS doesn't say.

Also vague is the future traffic and parking outlook for West Potomac Park, which the statement says currently functions in an "excellent" way for recreational users of the park.

By transforming the present one-way loop around the park into a shortened two-way road doubling back on itself, traffic volume would be increased, the statement says, but "the only effect will be a lessening in comfort and convenience which drivers will experience . . . "

Park visitors would also have to walk farther from their cars, since most parking would be banned from roadways and some 525 existing parking spaces would be shifted to a lot near the 14th Street bridge more than half a mile away.

The statement makes no mention of Washington's existing monument to the nation's only four-time president: a desk-sized block of white marble near the National Archives building, inscribed with Roosevelt's name. According to historians, it is all the memorial FDR said he ever wanted.