Mike,
You cannot do that. Both the interfaces are layer 3 interfaces and you can make them L2 and assign to a VLAN. You use those interfaces to trunk to some layer 2 switch and does the inter-vlan routing for you.
For example:
router#config t
router(config)#int g0/0
router(config)#no ip address
router(config)#no vlan-id dot1q 300
router(config)#int g0/0.300
router(config)#description ***VLAN300 subinterface***
router(config)#ip address x.x.x.x x.x.x.x
router(config)#encapsulation dot1q 300
router(config)#no shut
router(config)#int g0/0.400
router(config)#description ***VLAN400 subinterface***
router(config)#ip address x.x.x.x x.x.x.x
router(config)#encapsulation dot1q 400
router(config)#no shut
HTH,please rate if it does.
-amit singh