Please let me know the correct pronunciation of God Shiva's Beeja or moola mantra- is it hauh or hraum or haum?
Finally was able to get the needed reference from the book Sarva Devdevi Mantrakosha.
(This book gives numerous Mantras from the Tantras first in the coded forms and then decodes them into their chantable/recognizable forms. The drawback of this book is it's completely in Sanskrit without Bengali/English translations and it also does not specify which particular Tantra the verses given are from).
Atha Shiva MantrAh: --- (Coded) SAntamaukAra samyuktam Bindu bhustimastakam |
PrAsAdAkhyo manuh prokto bhajatAm kAmado manih | (Decoded) Haum |
So, as you can see first the Shiva Beejam or Mula is given in the code. To decode it we proceed as follows:
The 51st/last letter in Sanskrit is Ksha, so last but one (Sa+anta) is Ha. Add to it Au-kAra and finally add Bindu at the end/top : - This gives us Ha+au+m=Haum as the Shiva Bija Mantra.
Note that it also states that Shiva Bija is known as "PrasAda" too. That's why the Hamsa Mantra is known as ParAprAsada Mantra (ParAshakti+Shiva/PrasAda) in KulArnava Tantram.
I am giving few other Tantric Shiva Mantras along with:
Coded - Bhuvaneshi pranavam namaha shivAyah bhuvaneswari ||
Decoded - Hrim om namah shivAya hrim ||
Shadaksharah shaktiruddhah kathithohashtAksharohaparah .... ||
Decoded - Om hrim hauh namah shivAya ||
Mrityunjaya Mantra (short form) -
Coded -- TAram sthiro sakarnendubhriguh sarga samanvitah | TryaksharAtmA nigadito mantro mrityunjayAtmakah ||
Decoded - Om jum sah ||
Mrityunjaya (full form) -12 lettered
Om jum sah pAlaya pAlaya sah jum Om ||
DakshinAmurty Shiva Mantra -
Coded - Pranavam hridayam pashchAttato bhagavate padam .... ||
Decoded - Om namo bhagavate dakshinAmurtaye mahyam medhAm prajaccha swAhA ||
Note - Chanting these Mantras should not be done without first taking them from the Guru. Mantra chanting without knowing the limbs is also useless (and I have not given the limbs here). So, the info given here is only for the sake of answering.