Postmaster General Benjamin F. Bailar yesterday endorsed President Carter's concept of a new "citizen rate" for letters mailed by individuals, which the Postal Service executive described as a marked departure in postal rate policies.

In a formal proposal to the Postal Service's board of governors, Bailer said the first-class rate for individuals should be 13 cents for each ounce.

The 13-cent stamp for individuals, Bailer suggested, "could have a long life" if inflation eases and if the independent postal corporation is permitted to continue cutting costs, including a possible end to Saturday delivery.

All other first-class mail users - business and organizations which account for 80 per cent of first-class volume - would be charged 16 cents for the initial ounce and 13 cents for each of the next 10 ounces under yesterday's proposal to the board.

Currently, first-class mail costs 13 cents for the initial ounce and 11 cents an ounce for the next 12 ounces; under the Postal Service proposal, the new "citizen rate" would be 13 cents for each ounce.

Bailer told reporters the new "subclass" of rates for individuals would mean $300 million less in revenue than if the 16-cent rate were adopted for all users.

The changes are part of an overall rate increase package designed to bring in more than $2 billion in additional annual revenues to balance a projected deficit of $2.4 billion in the 12 months starting next March 25.

Included in the proposal are sweeping changes in the structure of postal costs for business users and periodicals as well as sharp increases for most categories - ranging as high as 62 per cent for special delivery stamps.

Bailers also proposed an expansion of discounted rates for large users who sort their mail before delivery to post offices and said innovations in parcel post rates will make the Postal Service competitive in some categories of packages with private delivery firms, such as United Parcel Service, (separate story, Page C13).

Governors of the Postal Service decided yesterday to postpone final action on the rate increase proposal until a special meeting scheduled for next Monday.

If, as expected, the board gives its approval, the proposal then will go to the independent Postal Rate Commission, which will hold hearings and must issue a decision within 10 months.Thus, if the higher rates and special "citizen" stamp rate are approved, they would not become effective until the middle of next May, at the earliest.

Although the idea of a special, lower rate for individual letters has been discussed by members of Congress and some postal users for serveral years, the last-minute inclusion of the "citizen rate" in yesterday's package was in response to a letter from the President to Bailar last week, following a White House staff study.

The U.S. Chamber of Commerce immediately denounced the "citizen rate" and several postal officials said they expect business groups to challenge it in court, if it is approved by the rate commission.

The chamber said the "citizen rate" adds up to "robbing Peter to pay Paul." Robert Hawk, director of the chamber's communications section, said that juggling rates on a preferential basis delays the eventual costs to individuals. "Any business . . . needs to charge rates for products or services that pay for the cost of providing them," he asserted.

In contrast, the National Association of Greeting Card Publishers applauded the idea, stating it was an early advocate "of a lower postal rate for the private individual, for whom the mails are the only feasible method of carrying on personal correspondence."

Bailar said that qualifications would be attached to the "citizen rate." For example, the sender would have to include zip codes on both the delivery and return address. Moreover, either the delivery or return address would have to be hand written - to prevent possible use of the lower rate by high-volume users.

The "citizen rate" would be available only for letters of standard size, shape and thickness. Printed bill envelopes sent by utilities or department stores 10 customers would qualify for the lower rate, provided users wrote in their return address, Bailar said.

On the question of Saturday mail delivery, Bailar said no decision has been made. He said meetings have been scheduled with postal unions to discuss possible work cutbacks associated with such a move, which he estimated could save more than $400 million a year plus 20 million gallons of gasoline by reducing deliveries to five from six days a week.

A proposal on the Saturday cutback, which would be the subject of public hearings, is expected later this year.