The White House took a cautious, wait-and-see attitude today to Soviet Foreign Minister Eduard Shevardnadze's surprise announcement he was resigning his post. ``It's not entirely clear what the situation is. We need to clarify that first'' before saying anything further, said White House spokesman Marlin Fitzwater. Asked if he thought Shevardnadze's decision was final, Fitzwater said, ``We don't know.'' ``I just talked to the State Department and we want to at least make sure we know exactly what's happened there'' before commenting further, the press secretary added. Secretary of State James A. Baker III has forged a close working relationship with Shevardnadze on arms control and on the Persian Gulf crisis.