Gov. Harry Hughes, stung by a series of legislative setbacks, launched an apparently successful lobbying campaign yesterday to save a key portion of his drunk-driving package from defeat in the Senate.

Hughes telephoned legislators yesterday morning and drafted several meaty amendments that later were appproved by a wide margin.

As amended, the bill would require breath tests for suspected drunk drivers except for drivers who are unconscious or must be hospitalized because of injuries. In those cases, a blood test could be administered.

The Senate earlier this month rejected Hughes' original proposal, which would have given police authority to choose which test the driver would take. (Drivers now may refuse to take a test). The bill was aimed at drug users, who now can opt for a breath test that will not reveal chemicals in their blood.

About 87 percent of the tests given in Maryland are Breathalyzers.

Sen. Francis X. Kelley (D-Baltimore County), urging approval of the amended proposal, said several hospitals in Prince George's County refuse to give the tests because they led to court appearances and administrative tasks.

Opponents, led by Sen. Thomas V. O'Reilly (D-Prince George's), argued that the blood test should not be excluded because it is more accurate, an issue that is hotly debated.