FRANK MANKIEWICZ and his fellow directors of National Public Radio have realized that no amount of electronic hand-wringing or lantern-rubbing will alter the hard, cold fact that the government's supply of hard, cold cash for public broadcasting is drying up. Rather than let the network evaporate, too, NPR is taking a number of financial initiatives to generate private money for its operations:

With a task force of prominent business leaders to help lead the charge into the private market, NPR not only will seek new and bigger contributors, but may establish or acquire profit-making subsidiaries--in all sorts of businesses--that could produce income for its nonprofit network. NPR already is prepared to market its satellite distribution system, enter into cassette sales and sell cable-audio services, with profits fed into programming.

To spur corporate giving, NPR plans to sell "shares" in special funds for programming--say, one fund for news and information, another for performances. Participating firms would be included in underwriting credits given at various times on the air during the broadcast day--not with any commercial praise for products and not tied to any specific programs, but rotated through all programming. Unlike an experiment about to be tried by a sample handful of individual public radio and television stations, NPR has no plans to accept any commercial advertising on its programs.

By eventually taking itself out of the bidding for government money, the NPR network may make it possible for all available federal appropriations to be directed to the individual local public radio stations across the country, to complement their private fund-raising efforts. So far, the network's new approach is receiving enthusiastic, bipartisan support from members of Congress who oversee public broadcasting. And why shouldn't it? If President Reagan is right about private corporations and foundations moving in to help where government moves out, National Public Radio will be in a good position to report on it.