关于setInterval启动但clearInterval不能停止的问题

[devil_tulip]

function setTimer(){
	var spanId;
	<%
	//startRecord
	//endRecord
	c = startRecord+1;
	while(c<=endRecord+1){
	%>
	spanId = 'num<%=c%>';
	if(document.getElementById(spanId)){
		if('' == $.trim(document.getElementById(spanId).innerHTML)){
			time<%=c%> = setInterval("getRandNum('<%=c%>')",10);
		}
	}
	<%
		c++;
	}
	%>
	//time1 = setInterval("getRandNum(num1)",10);
	document.getElementById("start").disabled = true;
	document.getElementById("end").disabled = false;
}

function ct1(showSpan){////////////////////////////////////////////////////////////////
	var divname = 'num'+showSpan;	
	if(document.getElementById(divname)){
		//alert('1');
		$.ajax({
			type: "POST",
			url: "setAction.jsp",
			data: {ac:'getRndNumAndSetOrder',rndOrder:showSpan},
			beforeSend:function(XMLHttpRequest){
				//alert('before');
         	},
			success: function(msg){
				//alert($.trim(msg));
				if('' != $.trim(msg)){
					clearInterval('time'+showSpan);
					document.getElementById(divname).innerHTML = $.trim(msg); 
				}
			},
			complete:function(XMLHttpRequest,textStatus){
				//alert('complete');
			},
			failure:function (result) {  
	            //alert('Failed');  
	        }
		});
	}
}

function ct(){
	<%
	c = startRecord+1;
	while(c<=endRecord+1){
	%>
	ct1('<%=c%>');
	<%
		c++;
	}
	%>
}

屏幕上数字在滚动，想要用clearInterval停止动作，可是按键后无法停止，需要在刷新后才会停止。目前我已经无计可施了，所以来请教下各位大神。