A huge Nashville media and entertainment company will announce plans today to build a lavish $560 million hotel and conference center complex in Prince George's County, a deal that would mark the largest single commercial investment in Maryland history.

The project is intended to anchor the National Harbor resort on the Potomac River waterfront just south of the Woodrow Wilson Bridge, and it will feature rolling indoor gardens, waterways and roaring falls crowned by acres of vaulted glass.

Gaylord Entertainment Co. officials have scheduled a news conference this morning in Oxon Hill to detail their agreement with National Harbor developer Milton V. Peterson. The announcement by Gaylord, which operates the Grand Ole Opry and the Opryland Hotel Conventional Center in Nashville, represents the first tangible indication that Peterson can deliver on a promise to build upscale restaurants and shops in a county starved for both.

"It's time we celebrated in Prince George's County with the kind of prosperity the rest of the region is enjoying," said County Council member M.H. Jim Estepp (D-Croom). "Having a company with that kind of resources and credibility just adds more credibility to the vision of National Harbor."

The conference center will feature 2,000 hotel rooms, 400,000 square feet of exhibition and meeting space, eight or nine restaurants and a number of boutique and other tony retail shops centered on an Americana theme, sources said. The 40-acre complex will include broad glass atriums much like those at the company's sprawling Opryland center, one of the largest hotel and convention facilities in the country.

The proposed center will be larger than the current Washington Convention Center but smaller than the one being built to replace it in Northwest Washington. By comparison, the Washington Hilton and Towers on Connecticut Avenue has 1,036 hotel rooms and 82 suites.

Development of the National Harbor site has already been approved by county officials. Construction is scheduled to begin this year and is to be completed by 2004.

The project is one of three that Gaylord has in the works in the country; it is building similar complexes in Orlando and Dallas.

"Man, it's going to be great," said Rep. Albert R. Wynn (D), who represents portions of Prince George's County. "Having this first step take place is just tremendous. The economic impact, the jobs, the enhanced image for the county are all positives, and it will be a nice place for our families to go."

Wynn met with company officials several months ago when they were negotiating with the Fairfax County-based Peterson Cos. Prince George's County Executive Wayne K. Curry (D) also has met with company officials, and he toured the Nashville hotel and convention center last year.

Curry declined to comment yesterday. He has said that the county will seek state funding this year to help with infrastructure costs associated with the development. But he has declined to disclose the amount or discuss the specifics of the request.

Del. Rushern L. Baker III (D), chairman of the county's House delegation, said a big company like Gaylord will make it easier to attract other investors to the site and should help the county get state funding. Gaylord's proposed $560 million investment would dwarf the largest private project undertaken in the state previously, Bethlehem Steel's decision to build a $318 million cold rolling mill at its Sparrows Point division in Baltimore.

"This is major for us, and that doesn't even come close to describing what this means," Baker said. "By bringing in a name like Gaylord, and given the numbers that they are going to invest, this is going to make National Harbor a state project. This will make it easier for us to sell it in Annapolis."

Peterson has had few difficulties winning over county or state officials for National Harbor. Curry and Gov. Parris N. Glendening (D) have wholeheartedly endorsed the development.

The County Council adopted special rules in 1997 to speed the development through the review process and then approved plans for the project a year later. Last year, Congress removed the final hurdle faced by the developer by eliminating federal oversight of the project.

The county has been trying for two decades to develop the property, which was once the site of a sand and gravel mining operation. Two other developers also won county approval for their grandiose projects. One had proposed a 52-story world trade center, and another planned to build town houses and nightclubs. But both ran into financial trouble before their projects materialized.

Peterson purchased the property three years ago from the federal Resolution Trust Corp., which acquired the land when developer James T. Lewis defaulted on a bank loan and turned over the deed to a San Diego bank that later failed.

Environmentalists have opposed plans for National Harbor because of its massive size and potential impact on traffic and on water quality in the Potomac River. Some residents also have expressed concern that the development will not serve the community.

"We don't want an amusement park in a residential neighborhood," said Helen O'Leary, president of the Indian Head Highway Area Action Council, a Fort Washington civic group that opposes the project. "It's a horrible thing to contemplate in the midst of a residential area."

But Del. Melony Griffith (D-Prince George's) said county leaders want the development to bring in tourists and their dollars--in addition to providing entertainment opportunities for the community.

"We see it as a marvelous opportunity for economic development, job creation and really getting Prince George's County on the national road map for tourists," Griffith said. "That's a good thing."

CAPTION: Gaylord Entertainment Co., which plans to build a hotel and convention center complex at National Harbor, operates the Opryland Hotel Convention Center in Nashville, above.