[yustaz]

clearInterval(intervalID:Number) : Void

вообще-то в документации все есть

//The following example first sets and then clears an interval call:

function callback() {
 trace("interval called: "+getTimer()+" ms.");
}

var intervalID:Number = setInterval(callback, 1000);

/*
You must clear the interval when you have finished using the function.
Create a button called clearInt_btn and use the following ActionScript
to clear setInterval():
*/

clearInt_btn.onRelease = function(){
 clearInterval( intervalID );
 trace("cleared interval");
};