The Government's battle to hold Phnom Penh is once again being hampered by shortages of supplies. American experts are saying that unless the United States Congress agrees to more military aid, the Khmer Army will actually run out of ammunition before the end of March.

A limited airlift, using U.S. Air Force aircraft on charter, is currently flying in 450 tons of ammunition a day. But the Khmer Government's forces are simultaneously using 600 tons of ammunition each day.

Although there are plans to increase ammunition supplies, it will probably be at the expense of food and fuel, which are also in short supply. There's so little rice about that many stall-holders in the city's largest market have closed down.

The problem hinges on the insurgents' hold on the Mekong River. The communist insurgents have now concentrated their efforts in preventing convoys getting through by river. Last year, only two ships were lost on the Mekong run. This year 16 vessels have been sunk or abandoned already.

So, with the roads cut, Phnom Penh's survival now depends on an increased airlift, flying in the daily requirement of 600 tons of ammunition, 500 tons of food and 300 tons of fuel. It would probably require 100 sorties by aircraft every day and the cost would be astronomical.