WASHINGTON (AP) _ Railroad workers have purposely jammed safety devices on trains at least 68 times since January's fatal Amtrak-Conrail collision near Baltimore, the head of the Federal Railroad Administration said Tuesday.

Federal inspectors have discovered 68 instances of the intentional disabling of warning whistles, electronic alerting devices and equipment that automatically stops trains, FRA Administrator John H. Riley told the Senate surface transportation subcommittee.

Riley said his agency's inspectors have found most of the tampering on Amtrak passenger trains, where they have conducted most of their examinations.

''I don't think this begins to measure what's happening on freight trains,'' he said.

Investigators have concluded that a whistle designed to blow when safe speeds are being exceeded had been taped over in one of the linked Conrail freight locomotives that smashed into an Amtrak commuter train in Chase, Md., on Jan. 4. Sixteen people were killed and 175 injured in the crash.

''Each of these was a Chase accident waiting to happen,'' Riley told the senators.

''This is crazy,'' Sen. Robert Kasten, R-Wis., a member of the panel, said of Riley's testimony. ''This is just absolutely nuts.''

After his testimony, Riley told a reporter that none of the reported tampering incidents resulted in an accident. He said he believed the devices were being jammed because train workers considered them to be a nuisance.

''I think we have people here who don't want any restrictions,'' he said. ''I think we have a cowboy mentality out there among a few people.''

J.R. Snyder, legislative chairman of the Railway Labor Executives Association, an umbrella group for the nation's railroad unions, said afterward that he would ask the subcommittee to provide him with details of Riley's figures.

Riley testified that to stop the incidents, the government needs the authority to take action against railway workers. Currently, the law only permits Riley's agency to take action against railroad companies, with a maximum fine of $2,500 per violation.

But Snyder told a reporter, ''If an engineer or any other crew member tampers with a safety device, the carriers should immediately take them out of service. ... These people get drastic discipline in these cases.''