Reagan backs voting rights - but

President Reagan's statement of support for the Voting Rights Act should help nudge the Senate toward action on extending this essential legislation. If only the Senate will be nudged.

As it is, the first subcommittee hearings are not scheduled until January, and opponents' delaying tactics could prevent compromise with the present House bill before key enforcement provisions run out in August.

Last year a fair housing compromise was killed in this way. Mr. Reagan has an opportunity to use his well-known clout with the Republican Senate to keep the Voting Rights Act on track. True, the law has always been opposed by a prominent conservative Reagan backer, Senator Thurmond, but it was endorsed earlier this year by another one, Senator Goldwater. The President ought to be helpful in bringing the whole Senate together on the matter.

Mr. Reagan's statement last week proved sensitive to the changing voting scene when he said: ''For this nation to remain true to its principles, we cannot allow any American's vote to be denied, diluted, or defiled.'' Impressive increases in black voter registration have been made since the act was passed in 1965. But some places have still sought to dilute minority votes by subtler means than banned practices such as the poll tax - means like gerrymandering or switching to at-large elections where these disadvantage minority voters. So need for the act remains. Thousands of legitimate election changes have been approved since the law was passed in 1965. But, of some 800 election changes objected to during this period, more than half were proposed in the last five years.

It is the provision requiring federal pre-clearance of such changes in all or part of 20 states that expires in August. The House bill would make the provision permanent. At the same time it would ease the ''bail-out'' conditions under which a jurisdiction can eventually win exemption from the preclearance requirement.

The House would also affirm that the act covers discriminatory effects whether or not discriminatory intention is proved. This provision would clarify Congress's meaning in view of the confusion left by two seemingly contradictory Supreme Court decisions on voting rights last year.

Mr. Reagan took some of the edge off his endorsement of extending the act when he favored a ''modified'' House bill. This seemed to mean a further easing of conditions for jurisdictions seeking exemption from the preclearance provisions. And he wanted the standard of discrimination to be intent and not effect.

We have commented before that a discriminatory result denies or abridges the right just as much whether its purpose can be proved or not. It is hard to tell how strongly Mr. Reagan feels on the point in a document which an administration aide reportedly said was deliberately ''flexible.'' He will honor his ringing defense of the right to vote by keeping the pressure on Congress for enactment but not seeking to water down the results.