In the early 1970s, as Vietnam War-era protests swirled around the Washington area, local police borrowed riot equipment and received intelligence training from an unusual source: the CIA. The agency, which is barred from domestic law enforcement, provided gas masks, stun guns, searchlights and protective vests. CIA specialists trained more than 20 officers ... in surveillance photography, countersabotage and surreptitious entry. The CIA-local nexus was included in hundreds of pages of documents released yesterday by the agency that detailed a quarter-century of CIA history. The records said the agency recruited officers primarily to protect CIA facilities from attack by protesters. A conscious decision was made . . . to utilize the services of local police to repel invaders in case of riot or dissension," a top CIA official wrote in May 1973. But the documents make it clear that the intelligence agency also wanted to keep tabs on the mammoth antiwar demonstrations in Washington from 1969 through 1971. The D.C. police department, for example, was given a communications system "to monitor major anti-Vietnam war demonstrations," the records said. The CIA aid also extended to basic law enforcement. Police officials in Montgomery County told The Post in 1973 that they received CIA surveillance training to combat street crime. The agency also gave Arlington and Alexandria a substance it had developed to detect whether someone had recently handled metallic objects, such as firearms.