Washington- The Food and Drug Administration on Friday approved the first HIV test that uses saliva rather than blood and delivers results in 20 minutes.

Public health officials hope the new test will encourage wider and more frequent testing. About 25 percent of all Americans carrying HIV, the virus that causes AIDS, do not know that they are infected, according to estimates by the Centers for Disease Control and Prevention. Around the world, that figure may be as high as 95 percent.

Although the test is as easy to use as a home-pregnancy kit and could eventually revolutionize HIV testing, the company, OraSure Technologies of Bethlehem, Pa., is not yet seeking approval for over-the-counter sales.

The OraQuick HIV-1/2 test is more than 99 percent accurate, said Michael Gausling, OraSure’s president.

The new test is “a very good thing,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and a prominent AIDS researcher.

Typical HIV tests require a vial of blood and are sent to a laboratory that returns results in two to 14 days. Two years ago, the FDA approved an OraSure test that used only a drop of blood from a finger-prick and gave results in 20 minutes; the company has since sold more than 500,000 of the tests, Gausling said. The new test uses the same technology and works as quickly, but with saliva, which is hundreds of times less infectious, and therefore less dangerous to the tester.

The company says the new test can detect HIV antibodies as soon after infection as earlier tests — roughly six weeks, though the time for each person varies.

For now, it can be used only in certified laboratories, but Dr. Lester Crawford, the acting commissioner of food and drugs, “strongly urged” the company on Friday to apply for a waiver that would let the test be used in simpler settings, like neighborhood clinics.

With such a waiver, OraSure’s Gausling said, “Anyone with a seventh-grade education can administer the test if they can read instructions.”