Several hundred employes and a number of patrons at a Library of Congress annex were evacuated from the building on Capitol Hill yesterday when a mix of chemicals being used in a renovation project spread toxic fumes, overcoming several construction workers.

One 22-year-old construction worker was taken to Capitol Hill Hospital shortly after 10:30 a.m., and was treated for a throat irritation and released. No other injuries were reported.

The threat of fumes, though, forced the closing of the library's Adams Building at Second Street and Independance Avenue SE for more than five hours. The annex houses two public reading rooms, as well as several library divisions dealing in reproductions and exhibits.

"It was noticeable," John Broderick, assistant librarian for research services, said of the fumes. "Until we could assess the situation, we told everybody to take a long lunch." Employes later were released for the day. The library reopened at 3 p.m. when late-shift employes reported to work.

Because D.C. Fire Department personnel were involved with a second chemical-related incident around the same time at the Martin Luther King Jr. Library downtown, hazardous materials workers from the Prince George's County Fire Department were brought in to handle the problem at the Library of Congress.

In the second incident, according to a D.C. fire spokesman, two trash haulers were exposed to chemicals apparently used in developing photographs while collecting garbage from a trash bin at the Martin Luther King Jr. Library at Ninth and G streets NW.

Both workers complained of irritation after they removed a one-gallon container of the chemical, spokesman Leo Givs said. They were treated at George Washington University Hospital and released.

Fire officials were unable to explain precisely how workers lost control of the chemicals they were using at the Library of Congress.

According to Prince George's fire spokesman Tony DeStefano, workers on the first floor of the Adams Building apparently had prepared a five-gallon mixture and were applying it as a sealant to a floor area about 30 to 40 feet square when at least two workers were overcome by fumes.