A Citation II flight crew lost several Nav and Autoflight capabilities when they suffered a loss of AC power shortly after takeoff in inclement weather. The opted to declare an emergency and return to their departure airport for maintenance.

Narrative

After a normal start we departed Runway 35 with an initial heading of 350 and began a climb to 5;000 FT. Between 3;000 and 4;000 FT in the climb in IMC and heavy rain the RED AC Fail light illuminated on the cockpit annunciator panel causing a MASTER CAUTION WARNING as well. At this time the autopilot disengaged; the altitude pre-selector went blank; the flight director disappeared and the #1 ADI tumbled. Within seconds the Number 1 Inverter Fail AMBER Light illuminated on the Annunciator panel.As the SIC was retrieving the abnormal procedure checklist for the AC Fail Annunciation; the #1 ADI came back up and stayed erect for about 15 seconds; during which time I cleared the MASTER CAUTION WARNING. During this time we were leveling at 5;000 FT in IMC when Departure cleared us to 16;000 FT and a heading of 340; and to expedite through 7;000 FT. I initiated a climb and within seconds; the MASTER CAUTION WARNING returned followed by a second tumble of the #1 ADI. While the SIC was running the AC Failure checklist; and we were passing through 7;000 I elected to return to the airport. I advised Departure we were having an electrical problem and it to standby. Departure asked 'are you declaring an Emergency?' to which I replied 'No; not at this time; however; we would like to return to the airport.' Departure replied 'we will go ahead and declare an Emergency for you at this time.' Departure then stated 'If able turn to a heading of 180 and descend at pilot's discretion to 6;000 FT.'We received several step down altitudes and vectors to intercept the ILS approach; were cleared to land; broke out of the bottom of the cloud layer; executed a normal landing and cleared the runway at Taxiway F where we were given a different Ground frequency in order to communicate with fire and rescue. CFR inquired if we had an onboard fire; or a smell of smoke? The First Officer replied no; that we had returned due to an electrical issue. They followed us to the ramp where a normal shut down was conducted. The discrepancy was written up and the aircraft turned over to Maintenance.