Ten Northern Virginia Democratic and two Republican legislative candidates have been endorsed by the political action committee of Virginia's largest teacher group.

The endorsements by the 45,000 members Virginia Education Association's political committee is likely to yiel both financial contributions and volunteer support to the candidates in the Nov. 8 electiosn for the 100-members House of Delegates.

In the race for the five seats in northern Fairfax County's 18th legislative district, the teachers backed incumbent Del. Dorothy S. McDiarmid and Raymond E. Vickery Jr., both Democrats, Del. Vincent F. Callahan Jr., a Republican, and Democrats Karetta B. Hubbard and Kenneth R. Plum. The cities of Fairfax and Falls Church as well as the northern half of Fairfax County are in the district.

In southern Fairfax County's 19th legislative district, the teachers supported only four candidates for the five seats that will be at stake in the election. Dels. Richard L. Saslaw and Thomas Jefferson Rothrock, both Democrats, and Del. Warren E. Barry, a Republican, won the group's endorsements along with Democrat Gladys B. Keating.

All the endorsements parallel those given previously by the political committee of the Fairfax County Education Association, a 7,000-member teacher group.

Three Democrats running for the three seats in Arlington's 22d district won "contingent" endorsements from the teachers. They are Dels. Mary A. Marshall, Warren G. Stambaugh and James F. Almand. The endorsements will meade final after a formal vote by an Arlington teachers' political committee, a step that a spokeswoman said is only a procedural.

The teachers also voted to donate $500 "debt reduction" gifts to two Northern Virginia delegates they supported in the June 14 Democratic primary. The funds will go to Dels. Ira M. Lechner of Arlington, who lost a race for lieutenant governor, and John L. Melnick, also of Arlington, who lost the race for nomination of attorney general.