The General Assembly, which opened its 1980 session last week, has completed appointments to standing commitees in the Senate and House of Delegates. Following are the committee posts held by Northern Virginia legislators. SENATE

Agriculture, Conservation and Natural Resources. Clive L. DuVal II (D-Fairfax), Charles L. Waddell (D-Loudoun), Edward M. Holland (D-Arlington), Charles J. Colgan (D-Prince William).

Commerce and Labor. DuVal, Holland, Colgan.

Courts of Justice. Holland, Joseph V. Gartlan Jr. (D-Fairfax).

Education and Health. Adelard L. Brault (D-Fairfax), Holland, Richard L. Saslaw (D-Fairfax).

Finance. Brault, DuVal, Colgan.

General Laws. Brault, Holland, Wiley F. Mitchell (R-Alexandria).

Local Government. Gartlan, Waddell, Mitchell.

Privileges and Elections. Brault, Gartland, DuVal, Mitchell.

Rehabilitation and Social Services. Gartlan, Waddell, Saslaw, Holland.

Transportation. Waddell, Holland, Saslaw.

Rules. Brault. HOUSE

Privileges and Elections. Mary A. Marshall (D-Arlington), Earl E. Bell (D-Prince William, Loudoun), Elise B. Heinz (D-Arlington, Alexandria), Vincent F. Callahan Jr. (R-Fairfax).

Courts of Justice. Floyd C. Bagley (D-Prince William, Loudoun), James F. Almand (D-Arlington), Bernard S. Cohen (D-Alexandria).

Education. Dorothy S. McDiarmid (D-Fairfax), James H. Dillard (R-Fairfax), David G. Speck (R-Alexandria).

General Laws. Heinz, Almand, Warren E. Barry (R-Fairfax).

Roads and Internal Navigation. Marshall, Bell, Robert E. Harris (R-Fairfax).

Finance. Warren G. Stambaugh (D-Arlington), David G. Brickley (D-Prince William, Loudoun), Martin H. Perper (R-Fairfax), John S. Buckley (R-Fairfax).

Counties, Cities and Towns. Marshall, Bagley, Gladys B. Keating (D-Fairfax), Cohen, Barry, John H. Rust Jr. (R-Fairfax).

Appropriations. McDiarmid, Callahan, Barry.

Corporations, Insurance and Banking. Keating, Callahan, Harris.

Health, Welfare and Institutions. Marshall, Stambaugh, Brickley.

Conservation and Natural Resources. Heinz, Brickley, Lawrence D. Pratt (R-Fairfax).

Agriculture. McDiarmid, Bell.

Labor and Commerce. Stambaugh, Pratt.

Claims. Bagley, Callahan, Harris, Perper, Rust.

Mining and Mineral Resources. Speck.

Militia and Police. Keating, Almand, Bagley, Dillard, Buckley.

Interstate Co-operation. Stambaugh.