Management of the U.S. Postal Service yesterday proposed sharp increases for most classes of mail, coupled with incentives to large-volume users to pre-sort their mailings and parcel post charges designed to make the nation's post offices more competitive with private delivery firms.

The rate package offered to the postal service's board of governors is designed to bring in more than $2 billion of additional annual revenues. Postmaster General Benjamin F. Bailar said first-class rates for most users should increase by an average 21 per cent, from 13 to 16 cents an ounce.

Other major proposals expected to be approved by the postal board next Monday and forwarded to the independent Postal Rate Commission for a decision within 10 months included:

The cost of post cards would go up 11 per cent to 10 cents from 9 cents, and the cost of pre-sorted post cards would go to 9 cents from 8 cents.

Large users who pre-sort first-class mail would get a reduction of 2 cents a letter from the 16-cent rate being proposed compared with a current discount of 1 cent a letter.

Second-class rates for newspapers and general circulation magazines would be increased by an average of 29 per cent. However, Bailar said publishers who pre-sort their mailings could win significant savings of some 20 per cent because their rate boost would be 19 per cent compared with 41 per cent for second-class publications not sorted in advance by ZIP code.

Bailar said another innovation for publishers would extend the setting of postal rates for newspapers and magazines according to the distance the publication travels. The current formula giving an advantage to publications with zoned editions whose advertising content varies now also will take into consideration variation in editorial content.

For nonprofit organizations publications, such as the National Geographic Society's magazines or the Boy Scouts' Boys' Life magazine, rate increases of 23 per cent: classroom publications, such as weekly current events readers, would face a 5 per cent boost.

Rates for third-class, bulk-rate mail (called advertising circulars and catalogs by the postal service and "junk mail" by detractons) would be boosted by 14 per cent while fourth-class rates for books and phonograph records would jump 34 per cent.

While average parcel post rates would be increased by more than 26 per cent, packages of 12 to 30 pounds each sent over distances of 1,000 miles or less would be cheaper in many instances than rates now charged by such private firms as United Parcel Service (which has boosted its own rates by 13 per cent this year in two steps).

If approved by the postal commission, the higher rates would provide annual revenues of $17.6 billion - about equal with projected expenses in the year starting next March 25.