Viejo Bancorp, the holding company for Mission Viejo National Bank, posted net income of $5,000 for the third quarter, a 97% drop from $195,000 earned in the same period last year. For the first nine months of 1987, the company reported a $888,000 profit, more than double the $333,000 earned last year. The earnings decline includes $775,000 in securities losses, but Viejo Bancorp President Jack R. Barnes said the company had closed out its stock positions by the end of September. As of the end of September, the company's assets were $54.2 million, a 36.9% increase from $39.6 million a year earlier. Total deposits grew 32.9%, to $48.9 million from $36.8 million a year earlier, while total loans rose 14.1%, to $31.6 million from $27.7 million.