The U.S. Postal Service is going to have to sell an awful lot of stamps to finance new pay and fringe benefits now in the works for 800 of its chosen executives.

Over the next couple of months the semi-independent government corporation will be offering 5,000 of its managers and executives the chance to complete for 800 billets in a new high-risk, high-reward executive corps called the PCES. It will offer pay and fringe benefits unheard of in other agencies. Among the sweeteners the service will use to lure executives into the new management team are:

A salary range matching the $25,000 to $47,500 executive pay spread in other federal agencies, with the chance for a few career employes to get as much as $66,000 a year. That is $19,000 more than Uncle Sam offers career workers in other government jobs.

Annual pay raises of up to $7,000 a year based on present pay ranges.

Lump-sum cash bonuses, in addition to regular pay raises, of between $5,000 and $10,000.

Free annual physical examinations.

Government payment of settlement benefits and other costs associated with buying or selling a house because of official business or relocation.

Full payment for the cost of relocating executives when they retire to any spot they pick in they United States or Puerto Rico or the Virgin Islands.

Generous death benefits to the survivors of an executive who dies before retirement.

Relocation payments in full for the family of an executive who dies before retirement.

Lump sum payments of up to $1,000 each for an executive, and two dependents, for "out of pocket" expenses associated with a move.

Two years of paid graduate study, and an 11-month sabbatical at full salary for PCES members who take training approved by the postal service, and who agree to work for four years after returning from study or leave.

Some of the fringe benefits-like bonuses and limited sabbaticals-are similar to those that will be offered civil servants in Grades 16 through 18 who elect to join the Senior Executive Service. It will be made up of top career and noncareer executives from nonpostal branches of government. Many of the things being offered by the USPS to its elite are eye-poppers that the rest of the federal establishment cannot begin to match.

Postal officials say the benefits being offered to PCES members are based on private industry fringes for top management personnel. They point out that the few who are chosen will be required to be mobile, and uproot themselves and their famlies to take various assignments.

People chosen for the PCES will get raises based on ratings of "good," "very good" or "outstanding." They will be worth from 4 percent to 9 percent for the lowest level of achievement, 7 percent to 12 percent for the "very good" and anywhere from 15 percent to 20 percent of salary for those who get "outstanding" marks from their bosses. In addition, 7 percent of those in the PCES also will be able to get special acheievememt awards worth from $5,000 to $10,000.