Two weeks after permanently closing part of Pennsylvania Avenue, Clinton administration officials are seeking an alternative to the ugly concrete barriers and barren two-block stretch of asphalt created in the rush to prevent a bomber from striking the White House.

They have turned to a group of 10 prominent architects and urban planners, among others, who have suggested that the closed section of the street be converted to a pedestrian plaza with fountains, benches, restrooms, trees, grass, raised flower beds and brick or light granite surfaces.

The future look of the president's front yard is such an important statement about the White House and its relationship with the American people, the architects and planners said, that administration officials should consider a national competition to design the plaza in the same way a plan for the Vietnam Veterans Memorial was chosen from 1,400 entries in 1982.

"It's very important how they do this," said J. Max Bond Jr., a New York architect whose buildings include the Martin Luther King Jr. Center in Atlanta. "A nationwide process would be ideal so people would have the sense that it was open and participatory."

After closing the street May 20 to vehicle traffic between 15th and 17th streets NW, administration officials are focusing on what do do with the space, who will lead the project and where the money will come from.

No plan for the future of the street was in place when President Clinton announced the partial closing of Pennsylvania because the White House Security Review, the panel set up to evaluate protection of the president, focused mostly on Secret Service procedures. Moreover, panel members said, it would have been pointless to devote a lot of time planning the future use of Pennsylvania before knowing whether Clinton would approve closing the street.

As a result, a makeshift collection of concrete barriers and geranium-filled planters was rushed into place. It has been widely criticized as repelling and oppressive by government officials, architects and ordinary citizens. D.C. Council member Jack Evans (D-Ward 2) said the area around the White House reminds him of Checkpoint Charlie, military police posts that had been set up by the Americans to control traffic between East and West Berlin when the wall divided the city.

The barriers should be replaced with more attractive planters, trees or an ornamental iron fence similar to the one that surrounded the park during the 1800s, the architects and planners said. They say the continuous line of masonry piers erected after the 1983 bombing of the Marine Corps barracks in Lebanon remind people of bombings and probably are no longer needed on the sidewalk in front of the White House now that the street has been closed.

Overall, the architects and planners share Pierre L'Enfant's original vision for the front of the White House when he planned the capital 200 years ago: the center of a large open, landscaped space. The Washington Monument and Lincoln Memorial are laid out in such a manner, which sets them off and invites people.

"It's a marvelous opportunity, it seems to me, to create a place for people instead of mechanized equipment," said George White, architect of the Capitol.

"This square could be a memorial in the way the Vietnam Veterans Memorial was a healing memorial to a heartbreaking war," said Vincent Scully, a scholar and professor of architecture and art history. "If we have to do this for security reasons, the square could be a place to remind people we are a nation of laws and peace."

Some part of the street would have to be retained for ceremonial reasons, including the Inaugural Parade, although the full six-lane width probably would not be necessary, the architects said.

Nicholas Quennell, a New York landscape architect, favors an informal approach to the pedestrian plaza that carries forward the character of Lafayette Square, with its trees, grassy areas and flower beds. A fountain could be built in the center of the street, lining up with the fountain on the north lawn of the White House. The street could follow a curved path to distinguish it, he said.

Restrooms with diaper changing tables would be an important amenity for tourists and others who otherwise would have to search nearby streets for a toilet, said New York urban planner William Hollingsworth Whyte.

Architect John Carl Warnecke, of San Francisco, has dusted off a plan he submitted to his friend President John F. Kennedy in 1963 that recommends a formal plaza where the street is now, with fountains on each end, long raised flower beds in the center and a light gray granite surface.

"The plaza would welcome the public, and it would become the people's very own public place for viewing the White House," said Warnecke, adding that concerts could be held there. Undoubtedly, the area would become a popular place for protests as well.

Warnecke said that a short tunnel could be built to carry traffic under the street, with the pedestrian plaza on top. This is how traffic problems were solved at other major intersections in the L'Enfant plan throughout the city, Warnecke noted.

Elizabeth A. Bresee, executive director of the White House Security Review, said the tunnel concept could be considered. But a tunnel might be expensive, she said, and would require the street to be closed anyway during construction. By the time it was completed, she said, "traffic will have already adjusted" to the street closing.

Warnecke said a 1984 study for President Ronald Reagan pegged the cost of the tunnel and pedestrian plaza at $40 million.

Georges Jacquemart, a New York transportation planner who studied the street closing's effect on traffic, said a tunnel would be counter to the effort to lure pedestrians to the plaza.

"This is the core of downtown Washington," Jacquemart said. "It's not a place I'd want to encourage more traffic to go through."

To pay for the plan, which could cost several million dollars, some of the architects and planners suggested a nationwide fund-raising campaign, with a prominent American heading the effort, as Lee Iacocca spearheaded the reconstruction of the Statue of Liberty from 1982 to 1986.

Before the plane crash and shooting incidents at the White House last fall, the National Park Service had begun developing a 20-year plan to redesign the White House grounds, Ellipse and Lafayette Square.

That plan, which had contemplated closing Pennsylvania Avenue in front of the White House, is proceeding under a $3 million appropriation from Congress, with a proposal scheduled to be made early next year.

The Park Service could take the lead in planning the pedestrian plaza, although that has not been decided.

An independent commission is another option.

"There's no rush to pick anyone," Bresee said. "This is the kind of thing we want to make sure we're doing right so people are proud of the solution and see that {closing the street} was a good thing to do."

Staff writer Linda Wheeler contributed to this report.