The American invasion of Laos pushed American casualties last week to their highest toll in five and one half months.

Fifty-nine Americans were reported killed in action and 42 more died of non-hostile causes, the highest U.S. casualty report since. September 5th. The reports attributed most of the casualties to the heavy support the United States is giving to the South Vietnamese invasion of Laos.

South Vietnamese headquarters said that North Vietnamese gunners had shelled three South Vietnamese bases inside Laos on Wednesday night. They also said that the North Vietnamese had attacked an artillery base and two ranger positions in the lower panhandle of Laos.

Field reports said six more U.S. helicopters were shot down or damaged in trying to defend the South Vietnamese ranger bases in Laos.

The South Vietnamese made no mention of ground fighting in the artillery attacks but did report two small ground clashes at other points inside Lacs.

In Washington, Defense Secretary Melvin R. Laird claimed that the South Vietnamese invasion, which began on February 8th, had not bogged down. "The operation is going according to plan," he said yesterday.

Four of the six American helicopters that were downed were hit Tuesday and two more on Wednesday at one of the ranger bases that the American-supported South Vietnamese are setting up in Laos. It was no reported how many of the six damaged helicopters were lost.

Invasion casualties since February 8th are 40 Americans killed, 26 wounded, 15 missing and 29 helicopters lost.