Candy bars got smaller and so did newspaper pages, magazines and automobiles in recent years, all to save money.

Now, the U.S. Postal Service has decided to experiment with the idea, part of a continuing program to reduce its operating losses.

Starting Jan. 12 in five cities - including Richmond - alministamp will go on sale in a test program scheduled to end in May.

Involved is a new, 13-cent stamp with an 1877 Indian head penny as the central design. Instead of the traditional image-area stamp size of 75 inches by 87 inches, the smaller stamps will be 54 inches by 66 inches.

A full sheet of the ministamps will contain 600 stamps compared with 400 in the normal format. Since about 3.6 billion sheet stamps are sold annually, the savings in paper costs could add up to $700,000 if adopted nationwide, postal official said.

There is one hangup to universal use of ministamps, however. Vending machines in use across the nation would be made obsolete if stamp rolls were made smaller.

According to a Postal Service announcement, the first ministamps and first-day covers for collectors will be issued Jan. 11 in Kansas City, one of the test sites. It will go on sale the next day in Richmond Portland, Ore.; Hartford and Memphis.

The stamps will be sold at all stations and branches in the five test cities and by 150 philatelic centers at post offices throughout the nation.

Testing in each of the cities will determine customer reaction to the smaller format, "with emphasis on ease of tearing and affixing stamps, and compatibility with mail processing systems in actual operation as opposed to a laboratory experiment," said the Postal Service in its announcement.

The paper savings projected by postal authorities would wipe out the $652 million loss with which the U.S. Postal Service operated in the last fiscal year.

However, forthcoming negotiations with postal workers on new contracts plus normal inflation are expected to result in higher costs and the need for greater federal subsidies with or with out the savings from ministamps.

Postage stamp increases have been proposed to take later this year along with inauguration of 2 "citizens' stamp," designed to maintain the 13-cents-pr-ounce first class rate for personal letters. It now appears that the "citizens' stamp" could be of the ministamp variety.