Speculation is running wild in this central African capital about the number of American advisers here and what they may be doing. According to a high-ranking United States diplomat, there are nine US military officials in Chad. ''We have four guys here who deal with the airplanes ,'' the diplomat explained, ''and five unloading US military equipment and overseeing its shipment in Chad.''
This same source says the four US soldiers arrived in Chad two weeks ago with the first shipment of US military equipment and ''will leave as soon as they are not needed anymore.''
US diplomats here say four ''noncombatant trainers'' arrived in Chad last week to help train President Hissein Habre's troops to use the 30 US-supplied Redeye anti-aircraft missiles. With those missiles now deployed in northern Chad , these trainers will ''will be leaving Chad in the near future,'' a US official here says.
(The Pentagon says the US has no more than seven military advisers in Chad. It, too, reports that three advisers have finished training Chad soldiers in the use of the anti-aircraft missiles and that the three will be leaving soon. The Defense Department says a three-to-four-member quality assurance team will be staying on in Chad a bit longer to make sure US military equipment functions properly.)
When asked if any of these US military advisers and technicians has seen any ''action'' in Chad, one US official threw up his arms, smiled, sat back in his chair and said, ''No, no. They haven't even left N'Djamena. What do you think this is anyways, Vietnam?''
But some observers think many more American military men are in Chad, and that their duties may go beyond those described by US officials.''
(President Reagan Thursday accused Libya of ''adventuring'' in Chad but for the first time ruled out any direct US military intervention in the landlocked African nation. The President said the US would not go beyond providing Chadian troops with equipment and training in how to use it.
(In northern Chad, the strategic town of Faya-Largeau was reported to have fallen Wednesday to the rebel troops of Goukhouni Woddei. Western military sources said a Libyan officer identified only as Major Massoud supervised the final assault on the oasis town, and that Libyan armor and infantry were primarily responsible for the town's capture.
(Chad Information Minister Mahamat Soumaila said, however, that although Chad's forces had withdrawn from the town of Faya-Largeau, they would not withdraw from the 50-mile-wide oasis surrounding the town.)