The Metro board tentatively agreed on a new schedule that will keep the subway construction program on track in Maryland, Virignia and the District of Columbia through 1981, but a Maryland official said he will oppose the plan.

Larry Saban, regional representative from the Maryland Department of Transportation, said the problem with the plan is that it lacks "any framework for a long-term guarantee of local funding for completion of the planned 101-mile subway system.

Translated, that means that Saban does not trust Virginia to continue paying into the Metro construction fund after the Virginia segments of the system are completed. Two subway lines in Prince George's County are scheduled to be completed after everything in Virginia.

If Maryland continues to oppose the plan and withholds local construction funds, about $350 million in projects will be delayed. Because of inflation, Metro officials argue, each delay adds costs to the current estimated price of a project.

The new schedule proposal was agred to by the District of Columbia and Virginia representatives, plus the Montgomery County representative yesterday. It had been under discussion for months.

Francis B. Francois, a Prince George's councilman and member of the Metro board, abstained, saying he couldneither support nor oppose the plan until he knew what the state of Maryland would do.

Saban said he is confident that some solution can be reached. If it is not, construction money will dry up beginning in July for the completion of some work on the Red Line extension into Montgomery County.

Fairfax County superviosrs Joseph Alexander and Marie Travesky promised yesterday that they would seek to schedule a county bond referendum in 1981 that would raise the local money for the short-term progress. That promise, however, did not solve Saban's problem.

The new short-term program would schedule a total of $323 million of construction work in 1981, including $79.2 million for new subway cars. The rest of the money would be spent to complete the Shady Grove line, to continue work on the Orange Line extension from Ballston to Vienna, to build the tubes under the Anacostia River from the Navy Yard to Anacostia, and to purchase rights of way in Prince George's County.