This years campaign could be the last hurrah for Willie Horton and his friends. The Massachusetts convict became a household name after an independent group called Americans for Bush ran ads telling how he brutalized a Maryland couple while on furlough from prison under a program approved by Michael S. Dukakis. But the Federal Election Commission has just voted to ban unauthorized use of a candidates name by political action committees. As a result, campaigns can no longer take advantage of Horton-like spots and at the same time claim to have nothing to do with them. The normal 3-3 partisan split on the fec was broken when the Administration, which is still taking flak for alleged complicity in the Horton ads, came out in support of the new rules. But to avoid mid-campaign disruption, the commission voted not to make the regulations effective until the 1993-94 election cycle. Still unresolved: how the new rules would restrict ads attacking opponents.