Hi Sandeep,
Check the BAPI_BUS2001_PARTNER_CREATE_M, where as this BAPI will helpful for Project def only.
check the SAP Note 638781 which helps in determining project authorization via partner functions.
check TCODE OPSPAR3 >Partner schema > Assign partner schema to project profile (OPSA)> this will provide you a tab as "Partner" in WBS.
also check below link:
BAPI / FM to assign IM Positions and Partners to WBS Elements
hope this will help you.
thanks
Sunil