The parish registers include records for the state religion (Lutheran) but also for "dissenters". Many of these registers were microfilmed for the FHL library, and later digitized and made available online through the Norwegian Digital Archives (Digitalarkivet). The Digital Archives make available newer registers that were not part of the Family History Library microfilms.
For the years 1896-1921, you may have to check both the Digitalarkivet links above to find the records you are looking for.
For events prior to 1856, check parish registers for Asker.
Note that Digitalarkivet includes searchable transcribed records for some of the registers - the transcription appears to be ongoing. The search has limited flexibility and does not appear to support soundex at this time.
FHL film numbers
These may be ordered through the nearest Family History Center.