Oh yes, they scoffed. Dismissed Prince George's County as the poor relation of the metropolitan area. Called the county a laggard in the region's economic development boom. Used the flippant nickname "P.G." with abandon.

But no more. This frog has turned into a Prince.

That was the message yesterday of the third annual County Planning Day in Upper Marlboro, attended by more than 350 county officials, politicians, developers and residents.

The title of the all-day session at the county administration building captured that optimistic, we're-up-and-coming theme: "Hello, Prince George's. Goodbye, P.G."

"What we've had to overcome was other people's perceptions of this county," said County Council Chairman William Amonett. "We knew we had the excellence and we always had the pride. Other people just had to see it."

The planning day comes at a time when Prince George's County is being hailed as a new frontier for area development.

In the county last year, new commercial development -- including stores, restaurants, offices, hotels and research facilities -- nearly doubled, according to the Metropolitan Washington Council of Governments.

Prince George's and Arlington were the only two of eight jurisdictions measured that showed gains over the previous year.

What's more, several immense new projects are in the works. They include PortAmerica, a billion-dollar commercial and residential complex on the Potomac River that will feature a 52-story skyscraper, the tallest building between New York and Atlanta.

In Bowie, residential and commercial construction worth a billion dollars is in the early stages, including a regional shopping mall that is being compared to the vast Tysons Corner complex in Virginia.

"Prince George's County has become a very popular place to come," Amonett said in his remarks to the group. "Thank heavens for that."

But the point of the program was to stress the importance of not just development, but also "quality development," easily the most frequently used phrase of the day.

The participants paid $10 in advance, $12 at the door, for the opportunity to sit in on workshops with such weighty titles as "Performance Zoning -- How Does It Work?" and "Changing Demographic Realities of the 1980s and Their Implication on Public Policy."

Phelps Freeborn, a research scientist and enthusiastic bicyclist who lives in Hyattsville, attended the program, he said, because he wanted to put in a word for bicycle routes.

Eloise Hall, representing the Carsondale Civic Association, wanted to find out about construction projects that might affect her community.

County employes wearing red carnations assisted people in finding their workshops. Displays in the lobby featured photographs of county historic sites, and the county beautification committee's 10th anniversary observance of "Bluebird Week."

Lunch was served, and the session was capped at midafternoon with wine and cheese, the presentation of awards, and again, a celebration of the county's emerging popularity.

"The history of Prince George's as the 'ugly sister' goes back many years," said county planning board member Samuel Botts. "At one time, development here was not as progressive as it might have been . . . . But now we're getting the Fortune 500 companies, while also being the kind of county where people like to raise children. It's top quality development now," he said.