I want to block port 80 from Lan use to make squid the default. i tried it with the ip tables but it's blocking web access completely that im not able to browse even with squid
Ttrasparent proxy thru squid. For this make your squid as a transparent proxy and redirect the request for port # 80 to 3128 like the following rule.
#iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 3128
This will do.