Generate A AutoInc With StoredProcedure

I need to create a StoredProcedure to calculate a field auto-inc.
Who helps me?
I tried many code, but i didn't have sucess.

My sample:

CREATE PROCEDURE SP_CT_ITEM
AS

DECLARE @CONTADOR NUMERIC(008)

SET NOCOUNT ON

BEGIN TRAN

SELECT @CONTADOR = CAST(NM1_PARAMETRO AS NUMERIC(008))
FROM PARAMETRO (UPDLOCK)
WHERE SIG_PARAMETRO = 'CT' AND GRU_PARAMETRO = '001' AND COD_PARAMETRO = 'ITEM'

UPDATE PARAMETRO SET NM1_PARAMETRO = @CONTADOR + 1
WHERE SIG_PARAMETRO = 'CT' AND GRU_PARAMETRO = '001' AND COD_PARAMETRO = 'ITEM'

SELECT @CONTADOR

COMMIT TRAN

GO

Thanks.

Marco
mapolitti@stecsoft.com.br