Washington's new $98.7 million Convention Center, the object of years of acrimonious debate and planning, will stage its gala grand opening today with a festive afternoon ribbon-cutting ceremony and a black-tie dinner for booked and prospective conventioneers flown in from 27 cities.

Edward Singletary, chairman of the Convention Center board, described the massive 800,000-square-foot facility on New York Avenue, between Ninth and 11th streets NW, as an "impressive new landmark in the nation's capital."

"The partnership between the District government and the private sector has laid the foundation for its successful operation, as well as exciting new economic development in Washington," Singletary said.

But not everyone who took part in shaping the project -- the eighth largest convention center in the nation -- is convinced it will be a major boon to the local economy and tax base.

Sen. Patrick J. Leahy (D-Vt.), who helped steer a scaled-down version of the center plan through the Senate after Congress rejected a far more expensive proposal, said this week: "The city reduced the project from a $200-million white elephant to a $100-million boondoggle."

Congress first authorized spending for the center in 1978, after long debate and with an eye to improving the city's convention trade and hotel industry.

The center's first event -- the five-day National Capital Area Auto Show -- will begin Jan. 5. So far, 48 events have been booked into the center in 1983.

Promotion-conscious center officials are splurging $100,000 on the grand opening, including the invitation-only events today and Saturday and a festive public open house May 13 through 15. Major airlines and Washington hotels and limousine services have contributed thousands of dollars worth of plane tickets, ground transportation and hotel rooms for about 100 prospective or actual clients who have been invited here from across the country to be wined and dined this weekend.

About 1,000 persons, including community leaders and politicians, were invited to the ribbon-cutting ceremony at 2 p.m. today, following a performance on Ninth Street by the high-stepping Cardozo High School Marching Band.

Mayor Marion Barry, D.C. Del. Walter Fauntroy, members of the D.C. City Council, Singletary and George W. Demarest Jr., the general manager of the convention center, will take part in the ceremony.

Tonight, about 450 people will attend a black-tie dinner at the center. The menu includes consomme', scallops, filet of beef and truffles. Four wines will be served to the guests, who will be given the chance before eating to board Tourmobile buses to survey the cavernous center interior.

The plush affair will be catered by Ridgewell's Caterers. The convention center's official caterers, Sportservice Corp. of Buffalo and Waters Catering Service Inc. of Rockville, won't have their kitchen operating at the center until next spring.