FIRST INTERSTATE <I> ESTIMATES BRAZIL RISKS First Interstate Bancorp said its 1987 pre-tax income could be reduced by about 33.5 mln dlrs if it decides to reclassify its 339 mln dlrs in medium- to long-term loans to Brazil as nonperforming. But the company stressed in a filing with the Securities and Exchange Commission that it believes it is too soon to reclassify the debt, despite Brazil's Feb 20 suspension of direct interest payments on medium- and long-term loans. "The corporation believes that it is premature to make a decsion to classify such medium- and long-term debt as nonperforming at this time," First Interstate said. But First Interstate said that if Brazil's suspension of interest payments continues, it may have to reclassify its loans as nonperforming and place them on non-accrual, meaning that interest previously accrued but not paid would be deducted from net income and interest would no longer be accrued. Besides its medium- and long-term debt, First Interstate said it also has 165 mln dlrs in short-term loans or trade lines in Brazil. As of Dec 31, 1986, nonperforming Brazilian outstandings were about 4.1 mln dlrs, it said.