The initial review of Wednesday's failed Pershing II flight test has focused on a problem that is not expected to delay the missile's December deployment in West Germany, according to Pentagon officials.

Engineers studying the test data at Martin Marietta Corp.'s Orlando, Fla., plant say they believe a premature blowing out of a piece of metal, called a thrust reverser port, that controls the second stage rocket engine probably caused the missile to tumble and break apart 70 seconds after it was launched.

This would require "a little fix," Richard D. DeLauer, Pentagon undersecretary for research and engineering, said Thursday. An Army spokesman said yesterday that a port "popping" was not a new event for a Pershing. In the already deployed Pershing Ia, four similar failures have occurred in its several hundred test and training shots over the past 15 years, he said.

Although this marked the fourth failure in 16 Pershing II flight tests, and the third in the last four, Army spokesmen remain confident that no problem requiring a delay in deploying the missile will be found in the just-completed test or in the final two.

As an example of how quickly fixes can be made, one official pointed out that the failure June 19, during the 13th flight test, was easily handled once the cause was determined. Then, a wire controlling movable fins that guide the warhead became overheated after it came in contact with an engine exhaust. The wire is connected to the warhead computer that directs the flight and the heat short-circuited the system. The solution was to bind the wire away from the hot exhaust.

In the five Pershing II production missiles that have been turned over to the Army, the wire has been "physically restrained" from the exhaust, according to an official. That process took about four hours per missile.

And the wire was shortened in the missiles that are still in production, the official said.

Any delay in the Pershing II deployment, even for obvious technical reasons, officials said, could have a harmful effect on the tense political situation that surrounds the schedule for the first nine missiles.

The 1979 NATO decision to place the first Pershings in West Germany in December required the Army to move up by one year its originally planned initial operating date for the missile. To accomplish that, the initial 28-shot test program was reduced by 10, with development tests run by the missile contractor, and operational tests using Army troops, being combined.

As an example of how that worked, the missile that failed had been turned over to an operational Army battalion at Fort Sill, Okla., in February and had been used for troop familiarization exercises until it was shipped to Cape Canaveral for the test.

It was fired Wednesday by an Army crew that will be assigned to Germany, a spokesman said.