Officials said yesterday that Robert F. Kennedy Memorial Stadium is structurally sound, a day after chunks of concrete peeled off the underside of the stadium's upper deck and struck empty seats below during a D.C. United game.

Stadium managers sought to play down any dangers posed to fans, saying that flaking concrete is to be expected in an arena as old as RFK Stadium, which opened in 1961. They said that regular maintenance usually takes care of loose concrete before it chips off.

But the chairman of the D.C. Sports and Entertainment Commission, which oversees the operation of RFK Stadium and the adjacent D.C. Armory, said he did not want "to minimize the significance" of the incident.

"We don't want anything dropping on anyone," said John L. Richardson, a lawyer appointed to the commission this summer by Mayor Anthony A. Williams (D).

Richardson, who spoke to stadium officials yesterday morning at the behest of the mayor, said he was told that staff engineers make regular visual inspections of the facility. He also said he was satisfied with the system in place.

"But it's obviously not fail-safe and unfortunately, whatever it was that came loose was not detected," Richardson said. The commission, which holds its next bimonthly meeting next month, will get a report on the incident from stadium officials, he said.

Small cracks in the reinforced concrete allow water to seep in and rust the steel rods used to support the concrete, said James A. Dalrymple, executive director of the commission. As the rods rust, they loosen the surrounding concrete, causing it to flake off, he said.

Dalrymple said the chunks probably landed on seat 1 of the eighth row of Section 310 in the stadium. The seat yesterday bore large scratch marks. At least eight chunks were recovered near the seat. The biggest was a jagged piece about the size of an adult hand and weighing several pounds.

"If it hit somebody it would do a lot of damage, no doubt about it," Dalrymple said. "Thank goodness it didn't hit anyone."

A similar accident occurred several years ago when a longer strip of concrete flaked off the upper deck, landing on fans at a Redskins game and injuring one man's ankle, Dalrymple said.

On Wednesday night, the concrete chunks fell during the second half of D.C. United's game against the Miami Fusion. Fans who were sitting nearby said they scattered when the chunks hit the seats.

RFK Stadium, opened in 1961 as D.C. Stadium, was the first cantilevered stadium in the country, Dalrymple said. He said the commission has done an adequate job of keeping up the stadium. The steel girders supporting the upper deck have been sandblasted and repainted. When the stadium's engineers or electricians notice flaking concrete, all the crumbling parts are chiseled off and the area then is resealed with concrete, he said. "It's a constant thing that you're watching for," he said.

Other signs of the stadium's age include broken seats and rusty screws supporting light fixtures, he said.

"I don't think the average fan is at risk any more than they are at [two-year-old] Jack Kent Cooke Stadium," Dalrymple said. "As long as you have concrete construction, everyone's going to have the same problems."

The stadium can hold about 55,000 spectators. About 11,000 attended Wednesday's game.

D.C. United, which has been the stadium's primary tenant since 1997, is discussing the stadium's condition in its current lease renewal negotiations, said Rick Lawes, a spokesman for the team.