With a dozen law enforcement agencies converging on Cambridge this week, security precautions for the 350th anniversary celebration will be greater than for any other Harvard event to date.

"If you take the security coverage at Commencement, and multiply it four times, you are getting an idea of what we are doing," said Harvard University Police Chief Paul E. Johnson, who is overseeing the coordination of security at all the celebration events.

Police locked all but one gate leading into Harvard Yard at 2 a.m. today and closed off Tercentenary Theater and several buildings in the Yard to allow trained dogs to search the area for "devices and explosives," said Harvard Deputy Chief of Police Jack W. Morse.

To meet the needs created by crowds, protests and visiting dignitaries, all of the department's 70 police officers are working overtime, with help from local and state police.

"Security represents a major portion of our budget for the 350th," said Thomas W. Stephenson '37, general secretary of the 350th celebration. He declined to give a specific figure.

Johnson said Harvard Police have also been in close cooperation with the FBI, Treasury Department Security, the Department of Alcohol, Firearms, and Tobacco, and state and local police. "It's just as complicated as the World Series," said Morse.

Following plans first laid over a year ago, hundreds of Cambridge, Harvard, Metropolitan District Commission (MDC), Boston and state police will be present throughout the celebrations, Stephenson said.

State, MDC, and Cambridge police will supervise traffic control, while Harvard police and federal agencies will watch over the 350th events themselves.

This additional manpower is required to handle the estimated 50,000 spectators expected this week. The visiting throngs remain the greatest security concern.

"Trying to get 18,000 to 19,000 people into the Yard at the same time, in addition to crowd dispersal after the stadium show, traffic, and lines, will be our biggest problems," said Johnson.

Police have erected a fence around TercentenaryTheater and will conduct baggage searches andcheck tickets at the entrances to the theaterbefore the convocations and concerts, Johnsonsaid.

Sever Hall will be closed to the public fromnoon Wednesday to noon Sunday. The rest of thebuildings surrounding the theater will be closedtoday and tomorrow from 2 a.m. to noon, with theexception of Widener Library, which will open at 3p.m. today and noon tomorrow.

Proctors living in Weld and Thayer have beenmoved to Massachusetts Hall until the celebrationis over, and police have ordered Thayer-basedHarvard Student Agencies to close during theconvocations.

Construction workers in the Yard said they wereinstructed to build special platforms in SeverHall to enable security officers to view theproceedings from Sever's high windows.

Traffic will be rerouted around Kirkland St.before today's address by Charles, Prince ofWales, and Mass. Ave. may be closed off tovehicles depending on traffic conditions duringthe day, Morse said.