The Navy is stepping up its efforts to counter the threat posed by the Soviets' new 40-knot titanium submarine, Pentagon sources said yesterday.

The fresh evidence that the nuclear-powered sun can outrun US. warships is spurring the development of advanced torpedoes and other antisubmarine weapons for US. aircraft, ships and submarines.

On Tuesday, for example, the Navy awarded contracts of $60.5 million to Honeywall and $53.5 million to McDonnell Douglas to design and build 15 lightweight torpedoes for testing over a three-year period.

The Soviet Union is already testing one of its 40-knot titanium submarines -- designated Alfa by U.S. intelligence officers -- and building five more, according to Pentagon executives.

Not only has the United States clocked the Alfa as going 40 knots faster than US. submarines can go but covert tracking of the submarine has indicated it can dive deeper than any US. sub.

Pentagon weapon specialists are split on the question of whether the Soviet intend to build a whole new fleet of titanium subs or call off the effort after six are completed.

"The Soviets aren't about to waste that much money on toys," said one Pentagon specialist who believes the Alfa being tested is the first of a whole new class of attack subs.

Although the Soviet sub is faster and can dive deeper than its American counterparts, it is also noiser -- a key vulnerability as enemy submarines hunt for each other in the depths.