A good way to test the post-election spirit of cooperation is to select a manageable but real problem -- one not intensely partisan -- that can serve as a laboratory. My suggestion would be the U. S. Postal Service.

It is a presence in every congressional district, so no party or region has any greater stake than any other. No one pretends that solving the financial problems of the Postal Service will be simple or painless.

But if an agreement can be reached for the pain to be shared across a broad spectrum, there will be a better chance of popular acceptance of actions that no one wants to take but everyone realizes are necessary. For example, some very small rural post offices will need to be consolidated with others. Postal workers and their unions will need to make some concessions.

Postal customers (all of us!) will need to accept some changes in service levels such as six-day delivery. Postal retirees (like me) will need to accept some revisions in pensions and benefits. And a few laws, such as the disproportionate payments for future retiree benefits forced on the Postal Service by Congress, will have to be changed. Postage will probably cost a little more than it does in almost all other developed nations of the world.

WARD LYNDALL, MINNEAPOLIS