Many allegations in the second volume track closely with charges that first surfaced in a 1987 Senate investigation. The C.I.A. is reluctant to release the complete 500-page second volume because it deals directly with contras the agency did work with.

According to the report, C.I.A. officials involved in the contra program were so focused on the fight against the Sandinistas that they gave relatively low priority to collecting information about the possible drug involvement of contra rebels. The report concluded that C.I.A. officers did report on drug trafficking by the contras, but that there were no clear guidelines given to field officers about how intensively they should investigate or act upon the allegations.

In all, the C.I.A. received allegations of drug involvement against about 50 contras or supporters during the war against the Sandinistas, the report said. Some of the allegations may have been specious, the result of Sandinista propaganda, American intelligence officials said.

It could not be determined from the C.I.A.'s records how many of the 50 cases were fully investigated. But the agency continued to work with about two dozen of the 50 contras, according to American intelligence officials familiar with the report. They said the report had found that the agency was unable to either prove or disprove the charges, or did not investigate them adequately.

American intelligence officials, who provided information about the report, declined to identify the individual contras who were the subjects of the drug allegations. But they did say that in addition to individual cases, the report found that drug allegations had been made against one contra organization, a group known as 15th of September. That group was formed in 1980 and was disbanded in January 1982.

The C.I.A.'s decision to classify this second volume has already been met with criticism in Congress. Senator John Kerry, Democrat of Massachusetts, who led a 1987 Congressional inquiry into allegations of contra drug connections, wrote a letter Thursday to the Director of Central Intelligence, George J. Tenet, asking that the report be immediately declassified.

Mr. Kerry, who has reviewed the second volume of the inspector general's report, said he believed that C.I.A. officials involved in the contra program did not make a serious effort to fully investigate the allegations of drug involvement by the contras.

''Some of us in Congress at the time, in 1985, 1986, were calling for a serious investigation of the charges, and C.I.A. officials did not join in that effort,'' Mr. Kerry said. ''There was a significant amount of stonewalling. I'm afraid that what I read in the report documents the degree to which there was a lack of interest in making sure the laws were being upheld.''