Frustrated by government secrecy, the families of American servicemen long missing in action are mounting another effort to pry loose some federal records they hope will end years of uncertainty.

It is an effort based on the conviction that classified government documents could contain reports of live sightings and other information that might disclose the fate of missing loved ones.Sadly, however, this undertaking represents the triumph of good intentions over good judgment.

A few days ago, Rep. John Miller of Washington introduced a bill that would compel federal agencies to declassify and release to the public documents pertaining to the more than 89,000 military personnel missing since World War II.

Called the Truth Bill, it would exempt from disclosure any information that might expose sources and methods of intelligence-gathering. Despite this safeguard, the measure still runs some needless risks, including the risk of raising false hopes.

The process of declassifying records would be enormously time-consuming as well as complicated and sensitive. The National Archives, after all, have 625 million pages of documents from World Wars I and II, Korea and Vietnam. None of the material is computerized. Someone would have to go through all those documents page by page.

No matter how painstakingly such work were done, it wouldn't be easy to separate truth from falsehood. During the Vietnam conflict, for example, reports of supposed live sightings of missing American servicemen were fabricated by warring factions in South Vietnam and Laos trying to discredit each other. Nor would it be easy to declassify such a large volume of documents without running the risk of inadvertently letting some secrets slip.

Besides, the government already releases such things as live-sighting reports to next-of-kin as long as the disclosure would not jeopardize national security.

If those pushing the Truth Bill were as candid as they should be, they would acknowlege the painful fact that the specific fate of many missing GIs never can be fully known. That's why Congress turned down this measure last year - and why the lawmakers should do so again.