The combined processing power of the machines will provide more than 460 trillion calculations, or teraflops, per second.
IBM said the two machines will have 50 percent more processing power than the combined power of all of the machines on the list of Top 500 supercomputers.
The new IBM machines will be known as ASCI Purple and Blue Gene/L.
ASCI Purple will have 100 teraflops of power and will become the Department of Energy's main supercomputer for the Advanced Simulation and Computing Initiative (ASCI), with likely uses including nuclear weapons research.
ASCI Purple is expected to be completed by the second half of 2004 and will occupy the space of two basketball courts. It will contain 12,000 IBM Power5 processors organised into 196 individual nodes, with 2.0 petabytes of storage and 50 terabytes of memory.
The Blue Gene/L machine, meanwhile, will be used for atmospheric research, including climate change and boast 360 teraflops of processing power.
Both machines will leapfrog NEC's Earth Simulator, which as 35.9 teraflops is the current supercomputer title-holder.