Under a national system of preclearance, a federal agency like the Department of Housing and Urban Development, or a comparable state agency, would have to approve these laws before they went into effec t. The town would have to show that the ordinance did not have the intent or effect of excluding pe ople of col or.

After reviewing the town’s information, the government agency would decide, within a certain amount of time, whether to object to the ordinance. (The Civil Rights Division at the Justice Department used a similar process to review thousands of proposed voting changes under the Voting Rights Act.)

To do this, agency employees would conduct interviews or solicit public testimony and comments about the purpose and likely impact of the ordinance. They could research local and regional data on race and income to identify people who would be affected, while taking into account which populations are moving into and out of the area. If the agency did not have enough information to reach a conclusion, it could ask the town for more data.

If it found that the ordinance was discriminatory, the agency would block it. Then the town would either modify it or discard it. But the ordinance would go into effect if the agency had no objections.

This idea could apply to policing, too.

Imagine that a local police department with a history of discrimination adopts a new stop-and-frisk policy. Under preclearance, this policy would have to be reviewed by federal authorities, or by an independent state agency, before it could be carried out.

As a condition of approval, the agency might insist on training police officers not to use race alone as a reason for stopping peop le unless they match a specific description from a trustworthy source. It might also bar stops based solely on people’s presence in a high-crime area.