Politicians, pollsters, pundits and patriots who agonize over low voter turnout in national elections ought to take a tip from the U.S. Postal Service. In addition to delivering the mail wonderfully well, the mailmoving corporation has come up with a system that ought to send reluctant voters racing to the nearest polling booth. What you do is simple: offer people $150 to vote.

The USPS and major unions (with one holdout) have signed a tentative contract covering more than half a million workers.

As an inducement to get its employes to decide on the contract quickly, the USPS is offering all full-time workers -- most represented by the two major AFL-CIO unions -- a ratification check of $150 each if the contract is approved within 45 days.

The contract promises them an estimated $4.8 billion in wage and benefit improvements through 1983, promises the USPS labor peace, and the rest of us higher stamp prices.

Some people think the contract is the greatest thing since sliced bread. Some think it stinks. That is for the union membership -- eight out of 10 workers belong -- to decide.

The postal service isn't telling anyone how they should vote, or even if they should vote. The options are clear: Accept the contract and take the offer, go to binding arbitration or go on strike and probably get fired. But without telling people how to vote USPS says that unless the contract is ratified in 45 days nobody gets the $150 cash payment.

The beauty of the system is that it doesn't cost the USPS a nickel. How, you say, can that be since all those $150 payments equal a lot of 18-cent stamps? Ask yourself who buys stamps.

There is a lot more to the proposed new contract settlement than the $150-if-you-vote-right-fast payment. It also provides:

A $350 lump-sum cash payment that is retroactive to July 21 of this year.

An immediate $300-a-year raise.

Another $350 lump-sum cash payment this time next year.

A $300 annual raise next July.

A $350 lump-sum cash payment effective in July, 1983.

A $300 annual pay increase effective in July 1983.

Cost-of-living payments that could pay $5,000 over the three-year period if the current rate of inflation is maintained.

Improved retirement computations for workers eligible to retire during the life of the contract.

Unions say the average postal salary now is $21,146. Combined payouts and raises, plus COL adjustments in the proposed contract could boost that to over $27,400 (more or less depending on inflation) by the end of the contract. Workers will get those increases no matter when the contract is ratified, if it is ratified. But postal officials are counting on the $150 carrot, up front, as the clincher to make sure the contract is ratified fast.