so i was wondering...... the l239d chip can only tolerate 1amp right??? and l238 can tolerate 2amp ....so what if i use two relays to control a motor(one for each direction) i mean it would have atleast 10 amp!!! so it can control big fat motors like this one! 15000RPM DC Motor 12V 25000RPM DC Motor 12V [RKI-1228] - ₹230.00 : Robokits India, Easy to use, Versatile Robotics & DIY kits ...the relays are cheap and can tolerate a lot right ??!!! so what do u guys think?
I'm going to break this post up a little bit "backwards", starting with the last question first:
francisroan:
so what do u guys think?
I think you need to have some patience, and slow down a bit, because all of your numbers are confused and don't make any sense. You keep going like you are, and you are likely to either find a fire on your hands, or a small explosion, or both. Patience is a virtue, remember... 
francisroan:
so i was wondering...... the l239d chip can only tolerate 1amp right???
I think you mean the L293D? The L293D can only output 600 mA continuously (the L293 can output 1 A continuously - they are two different parts). Note that these numbers are only valid for an L293(D) with a proper heatsink attached.
francisroan:
and l238 can tolerate 2amp
Correct me if I am wrong, but I think here you mean the L298. The L298 can supply up to 2 A of current continuously on -each- of its h-bridge outputs (there are two in the chip - so it can control two motors); those outputs (and the inputs) can be "bridged" to allow the L298 to supply a -single- motor up to 4 A continuously. Once again, this is only with a proper heatsink for the L298. Also - you can't "bridge" the L293; it isn't designed for it, and will probably burn it out if you try. What you can do (although this isn't in any datasheet - but I've seen enough people do it) is "stack" multiple L293 chips together to parallel multiple chips into a single "block" to increase current capability. The problem with this "method" is that 1) it is outside the spec, and 2) heat from the "lower" chips is difficult to remove properly; ideally you should just avoid it. I have never seen this "stacking" method used with an L298, probably due to it's pin layout (you can't really stack the common multiwatt version), plus heat removal would be an even greater problem, likely. Ideally, you should avoid it. It's a hack, more than anything, when it works at all.
francisroan:
....so what if i use two relays to control a motor(one for each direction) i mean it would have atleast 10 amp!!! so it can control big fat motors like this one! http://robokitsworld.com/index.php?main_page=product_info&cPath=2&products_id=208 ...the relays are cheap and can tolerate a lot right ??!!!
-Which- relays?
You have to size the relays (contacts) for the load in question, just like any other component; any old relay won't do. Assuming you have a properly sized set of relays, though, then yes, you could control a motor's direction with relays (you will, of course, need to add other components to control those relays, like transistors or mosfets, flyback diodes across the coils, base/gate resistors, etc - for each relay). You would also lose the ability to control the motor's speed (since you can't use PWM with a relay). In theory (though I've never seen it done), you could put an NPN (like a 2n2055 or similar) on a beefy N-channel mosfet between the relays and ground and PWM that to control the speed thru the relays, but given all of the complexity of that, you would be better off to build (or buy) a larger all transistor/mosfet h-bridge.
If you don't care about speed control, though, then a pair of SPDT relays would work perfectly fine; commonly available automotive relays would be your best bet for use with larger motors (up to about 20-30 A). They are inexpensive, easy to source, and can handle high currents in a rough environment.
all the things u said was right(i was in a hurry)....but my idea is good right?