Rome wasn't built in a day. And neither has the United States completed the drive to end injustice against blacks and other minorities in the 20 years since the Rev. Dr. Martin Luther King Jr.'s march on Washington - a relative ''day'' in the history of human injustice.
It is gratifying that enormous progress has been made. But more is needed: Not fully resolved are issues of housing, education, and jobs. In a few communities even the voting rights of blacks still are in question. Overall, there is a feeling among blacks that latent prejudice remains among many whites.
In the past the US Civil Rights Commission has monitored both the progress toward racial equality and the continuing need. It is a very useful function whose continuance is in jeopardy: The commission's mandate to exist has expired, and proposals to continue its life are enmeshed in arguments over its makeup.
That is unfortunate. The long view is clearly called for: The commission continues to be needed and its existence should be extended. Reasonable men ought then to be able to settle the details, including the current disputes of whether President Reagan acted properly in replacing three commission members, as he did Tuesday, and whether the membership should be enlarged from six to eight. At base the issue is the relative power of Reagan appointees and holdover members, but that would be irrelevant if there no longer were a commission.
The question of the commission's future now is before the US Senate. Over the weekend there were reports that Senate Republican leaders had agreed to move quickly on a bill to extend the commission. However, by Monday morning the first move - action in the Judiciary Committee - had been postponed when, a committee representative said, chairman Strom Thurmond (R) of South Carolina failed to get the needed quorum to call a meeting Tuesday.
Senator Thurmond should get members to agree to meet forthwith. The proposal should be approved, and the commission should be continued.