Attorneys for Vietnamese orphans who were passengers in the 1975 crash of an Air Force cargo plane outside Saigon have accused the U.S. government of deliberately concealing photographs and movies of the accident, which they say support the children's lawsuits for money damages.

The charges, filed last week in U.S. District Court, are the latest round in the massive and bitterly contested damages cases brought in behalf of the orphans against the federal government and Lockheed Aircraft Corporation, which built the jumbo C5A transport.

The plane crashed into a marshy rice paddy, killing 135 of 330 persons aboard, including 76 of 226 orphans, in a tragic end to a highly publicized mercy mission at the close of the Vietnam War, known as "Operation Babylift." The attorneys claim most of the orphans, who were infants at the time of the accident, suffered brain damage as a result of the crash.

Close to $2 million was awarded by juries to three orphans after their cases went to trial. But the complex litigation (116 lawsuits are pending in Washington), was ordered to start all over again last May when the U.S. Court of Appeals threw out the awards and ordered new trials. The first retrial is scheduled to start today before Judge Louis F. Oberdorfer, following unsuccessful attempts to settle all of the cases out of court.

In papers filed in federal court last week, the attorneys said that the new evidence about the crash was produced by the government in September -- five years after it was first requested -- following a 45-minute search of a file room at Travis Air Force Base in California. The room had been used by a military accident investigation board.

The children's lawyers contend that the new photographs undercut Lockheed's argument that the crash applied no more force on the surviving children than would a normal landing. They contend that the photos show instead violent impacts with the ground. Moreover, the attorneys contend the pictures reveal that the troop compartment, where most of the children were located, was exposed to fire and fumes, which Lockheed denied.

The photographs were found in a black loose-leaf notebook on a bookshelf in the storeroom at Travis, attorneys for the children said in court papers. The pictures apparently had been overlooked by the Air Force officer who, in 1977, burned cartons of documents related to the C5A crash. The documents were destroyed in accordance with government regulations that require the destruction of all non-permanent documents after two years, court papers said.

The military officer who found the photographs in September said in a sworn statement that a thorough search of the file room would have produced the records earlier, according to court records filed by the children's lawyers. Those lawyers contend that the government deliberately avoided searching for photographs related to the crash.

The lawyers want the court to impose civil penalties on the government and Lockheed -- including attorneys fees and costs -- for their failure to disclose the photographic evidence promptly.

Mark Dombroff, the Justice Department attorney supervising the crash cases, and Carroll E. Dubuc, the lead attorney for Lockheed, both declined to comment on the allegations by the children's lawyers. A formal response must be filed with the court within the next week. Under the terms of a secret agreement, the government and Lockheed are sharing the costs of any damage awards made to the orphans.

Attorneys for the children contend that the trauma of the crash coupled with a shortage of oxygen resulted in the surviving orphans suffering brain damage. Today they suffer from learning disabilities and impaired motor skills as a result, the lawyers argue.

Lockheed's lawyers contend, however, that the children's illnesses, if any, were caused by poor care at orphanages in Saigon where they spent the early months of their lives.

Although the children's lawyers first requested all available photographic evidence in 1976, the Air Force officer in charge of the records room was not contacted by the government until 1977, after the destruction policy had been implemented, court papers said. Eventually, the children's lawyers said the government produced seven color slides showing aerial views of the crash for use in their case.

Since that first 1976 request, the children's lawyers contend that the government and Lockheed have repeatedly insisted they had no knowledge of any other documentary evidence. But the orphan's lawyers contend that the government delayed complying with demands for production of all documents related to the crash and also made no effort to block destruction of those records even though the lawyers' demand was pending before the court at the time.

"If good faith had been exercised by the government, the appropriate individuals would have been alerted in 1976 not to destroy the photographs" until the court resolved the issue, court papers said. Attorneys for the children also contend that Air Force regulations require that documents related to court cases be preserved for two years after the case is closed.

The new photographs and movies were discovered after the children's lawyers were told for the first time that the documents were destroyed. They then demanded that they be allowed to question an individual who would have knowledge of any available photographs, slide or movies of the crash.

Shortly thereafter, the government produced 800 pictures of the crash, two 16-millimeter moving pictures related to the C5A crash, 42 color slides and 35 color prints. No pictures of any of the dead or injured children have ever been produced, the attorneys said.

The children's lawyers also allege in court papers that Lockheed employes knew of the existence of still photographs and movies related to the crash. But Lockheed lawyer Robert P. Barton said in a sworn statement that he narrowly interpreted the lawyers' demands for those documents to mean pictures in Lockheed's possession related to the children's injuries. Barton testified he did not investigate whether Lockheed "knew of" photographs.