The chairman of a task force studying changes in the state's vehicle emissions testing program said yesterday that screening should be required every two years instead of annually, and continue to be offered at central testing sites.

House and Senate committees weighing proposed changes in the emissions testing program also heard from a Jiffy Lube executive who said his company's franchises want to offer the emissions tests along with oil changes.

Legislation offered by the Schaefer administration would require the tests every two years and would include an additional check to ensure the vehicles have not been tampered with.

The bill also calls for eliminating the waiver that excuses motorists from meeting the emissions guidelines if they spend more than $50 on repairs, and requires gas-powered trucks and vehicles up to 26,000 pounds to test their emissions systems.

Richard Berndt, who chaired the task force studying emissions, told the House Environmental Matters Committee his group recommends continuing conducting the tests at designated centers, instead of authorizing service stations to perform the tests.

Berndt said the group also considered whether the state should assume control of the tests, but decided a private contractor "would do this work in a more efficient manner."

The program, started in 1979, runs out at the end of 1988 and is designed to make Maryland meet federal air quality standards. Tests are required in Baltimore and seven Maryland counties and affect 1.7 million cars.

Tom Andrews, deputy secretary with the Department of the Environment, said hydrocarbons and carbon monoxide have been reduced by 90 percent in the Washington area because of the emissions requirements.

Systems Control of California operates the testing program for the state and has 10 stations in the Baltimore and Washington areas.