Last week, Robert Adams Jr., an 18-year-old graduate of Coolidge High School in Washington, took a temporary job with a demolition firm gutting the insides of the historic Willard Hotel. He planned to work several weeks, while waiting for his Army enlistment papers to be processed.

Adams, who had not yet taken home his first paycheck, was killed Wednesday on the 11th floor of the Willard when a wall and ceiling collapsed. He suffered a fractured skull and was pronounced dead at George Washington University Medical Center.

After a few days on the job, "Robert said the building was shaky, and that he didn't like that type of work," said his grandmother, Betty Fair, "but he said at least he would have a little money when he went in the service."

The death was the second major accident in less than a week on the work site of the $100 million Willard renovation project, the centerpiece of redevelopment along Pennsylvania Avenue. Last Friday, a brick wall at the rear of the hotel collapsed and demolished a construction crane, but no injuries were reported.

In Adams' case, officials of the federal Occupational Safety and Health Administration and the D.C. Office of Occupational Safety and Health said yesterday they are investigating whether the company, Regina Construction Corp. of Alexandria, had given Adams proper training and safety equipment, and whether the job was properly supervised.

"This worker was there only a few days, and the other two on the 11th floor job were only there a little over a month," said Lawrence Liberatore, OSHA's area director. "We are looking very closely at the type of training; how they did the job; what they were told by the foreman; and how closely they were supervised."

Details of the accident remain sketchy, officials said, but preliminary reports indicated that two other workers were knocking down the wall while Adams, who was not part of that project, was dangerously close.

"It seems to me as a safety person that they should have cordoned off the area and not allowed anybody in there unless they were part of the crew . . . and knew what they were doing," said Robert Anderson, supervisor of safety specialists in the D.C. office.

Officials of Regina and of the Oliver T. Carr Co., the project developers, were not available for comment. But phone calls to Regina were returned by Cranson Gates, a spokesman for a subcontractor on the project, Independent Services Ltd. Gates said yesterday that the 11th floor area where the collapse occurred had not been cordoned off.

"In hindsight," he said, "that might have prevented the problem."

Gates said workers were told of the danger of collapse Tuesday, and were told that the delicate process of removing a section of interior wall and ceiling would have to be done by a machine because of the danger. After the initial machine effort failed, he said, two workers tried to take down the section with sledgehammers.

"Adams just happened to be walking by" when the brick wall and terra cotta ceiling collapsed, Gates said.

Based on the fatality and the earlier accident, OSHA plans a "comprehensive investigation" of the entire Willard site, said Liberatore.

Adams' cousin, Joseph Watson, 21, who has also worked on demolition projects, said yesterday that the family is particularly bitter about the accident.

Adams had completed three years of ROTC training at Coolidge, his grandmother said, and had planned to pursue a military career.