Hi Rajasekaran,
I don't think it is possible to split the write off document number at VTREF level. If it is a must for you, you can always give VTREF number as input screen of write off General Selections -> Custom Selections. In that case you have to run the FP04M multiple times, once for each of the contracts.
On the otherhand, I am assuming your contracts are having different account determination IDs. So, as per posting area 0120, you will anyways have separate revenue/expense accounts posting even if you have a single write off clearing document created.
The write off document will post the receivable/payable GL account as per the source items that you are writing off. And it will post at expense account /revenue account as per the account determination ID of the source document.
Is your multiple FICA document requirement is based on anything other that GL posting?
Thanks
Bodhisattwa