Rejecting the advice of congressional auditors, Defense Secretary Harold Brown has ordered production of the troubled XM1 tank to start later this month, it was announced yesterday.

Percy Pierre, the Army's research and development chief, acknowledged at a news conference that "testing has not demonstrated the reliability we would have liked at this point."

But, Pierre said, delaying the $9.8 billion program now could cost more later.

A new gas turbine engine, never before tried on a tank, has suffered failures on several test models of the 58-ton XM1.

The tank also has transmission trouble that caused it to stick in reverse at its unveiling ceremony last year.

The problems led Congress' General Accounting Office to recommend in an April 12 letter to Brown that "it would be preferable to defer the initial production decision until there has been a demonstration through further testing that design changes and modifications have indeed corrected the problems."

Pierre said Brown considered that recommendation, but there was "nothing in that report we did not already know." He said Brown decided to go ahead with the first 110 production models this year.

Deliveries will start in February and the first operational XM1s should be with U.S. troops in Europe the year after.