FIRST THE NECESSARY caution about reading too much into a couple of political results -- and then on to the politically juicy question in Virginia this week: What messages were, and are, in the primary defeats Tuesday of two veteran influential state legislators by challengers who enjoyed considerable black voter support?

The most direct and sure result is a realignment of power in the state legislature. The two losers were top Old Guard members of key house committees. Del. L. Cleaves Manning of Portsmouth, defeated by 32-year-old Kenneth R. Melvin, had been expected to take over the chairmanship of the House Appropriations Committee. Del. Claude W. Anderson Jr. of Buckingham, who lost to Watkins Abbitt Jr., son of that area's former longtime congressman, was chairman of the Privileges and Elections Committee.

Next in order of likelihood is a change that would increase the legislative influence of Northern Virginia and the far southwestern area of the state. Del. Dorothy McDiarmid of Fairfax now becomes first in line to head the appropriations committee, which oversees Virginia's budget, though she does face Republican Jean Morrison in November. Del. Ford C. Quillen of Scott County is now in line to take over the privileges and elections committee. Another beneficiary of these shifts could be Del. Mary A. Marshall of Arlington.

Less clear but equally intriguing is the increased impact of black voters on these Democratic primary decisions and -- here's the biggest question for this year -- the effect on the November elections for governor, lieutenant governor and attorney general. Mr. Melvin, who defeated Mr. Manning, is black; Mr. Abbitt, who defeated Mr. Anderson, actively sought black support.

All sorts of factors besides race affect the decisions of voters in these local contests -- none of which may have much bearing on statewide general elections. But what should be becoming increasingly clear to politicians and voters all over the state is that every vote counts equally -- whatever the race of the person who cast it.