One of the best-paying, most important jobs in government may be filled today. To get it, you need to do two things:

1 Convince the U.S. Postal Service's board of governors that you are worth $63,000 a year and would make a good postmaster general of the United States.

2 Be prepared for a rotten summer.

The vacancy came up earlier this month when Postmaster General Benjamin Franklin Bailar - three years to the day he took the top mail-moving job - said he wanted to move on. And as quickly as a replacement can be found.

Today, at USPS headquarters, six members of the board of governors (all appointed by Presidents Nixon or Ford) will mett, to talk about upcoming contract talks with postal unions. They also will discuss, and maybe pick, a new postmaster general.

Some people believe that the next postmaster general could wind up being public patsy No. 1, little more than a $63,000 stand-in candidate for a political firing squad. Some believe that is why Bailar (who had a better job offer from industry) decided to bow out before the problems got worse.

The problem is that the USPS, a quasi-government corporation, must come to a new labor agreement before mid-July with unions representing virtually all its 600,000 rank-and-file workers.

USPS officials say they can not match the current 3-year contract, which provides increased fringe benefits, four pay raises, six cost- of-living raises and a promise that nobody working for the USPS would be laid off. The unions say they had better get similar agreements or there will be a strike that could stop the nation's mail service.

Postal officals say that they must make some service cuts (and that means layoffs), and want more automation and other changes to save money. The alternative, they say, is that the public will have to pay a lot more than 13 cents for a first-class stamp (USPS already has requested that it go up to 16 cents).

Observers feel that the next postmaster general cannot win, since he either will have to preside over a giant rate increase or a postal strike. Neither action is likely to endear him to the American public.

Members of the board of governors, who will pick the next PMG, work part-time. They get $10,000 a year, plus $300 a meeting, plus expenses. There are three vacancies on the board, which now includes a university professor, a cattleman, a Honolulu real estate executive, an investment banker, a president of an iron works, and an oil company official.

After talking about the upcoming labor negotiations, the board plans to discuss a successor to Bailar. Some people think that after the discussion of the labor picture, the board will conclude that it cannot find anyone qualified who is willing to take the heat for $63,000 a year.