An offer by a unit of Computer Associates International valued at $12.37 per share will be made no later than Friday, according to an agreement reached with Integrated Software Systems Corp. of San Diego. The deal has a total value of about $68.4 million. If the deal is consummated, ISSCO will become a subsidiary of Computer Associates and likely will drop its name, company officials said. The tender offer will be contingent on holders of at least 91.6% of ISSCO's 5.53 million shares approving the purchase. Computer Associates already has 40% of those shares secured under an agreement with some of ISSCO's key officers and directors.