The District of Columbia government defended its new regulations on street vendors yesterday and asked a federal judge to dismiss a lawsuit filed by a labor union representing vendors.

At a hearing in U.S. District Court, Robert J. Harlan Jr., an assistant D.C. corporation counsel, said the new rules were necessary to protect consumers and enhance the appearance of neighborhoods as well as to "reorder the balance between street vendors and stores."

The rules, scheduled to go into effect May 15, have been challenged as unconstitutional by Local 82 of the Service Employees International Union. A spokesman said about 150 vendors have joined a new vendors division of the union in the last month.

Yesterday J. Lincoln Woodard, a lawyer for the union, argued that the new regulations violate the equal protection requirements of the U.S. Constitution because they treat street vendors differently from stores. Woodard referred to the stores as "storefront vendors."

Judge Thomas A. Flannery responded that there was a long line of court decisions giving local government "broad discretion" to regulate economic activity. But he seemed more sympathetic to the union argument that the city could not severely restrict the merchandise that vendors may sell without showing that the sales might endanger public health and safety.

Flannery added, "I don't think it is a legitimate objective for the District government to protect shopkeepers from competition from street vendors." But the judge added that "there may be other objectives" in the regulations that do have a reasonable basis.

Flannery promised to rule on the case before the regulations take effect.

The new regulations, issued by the D.C. Department of Consumer and Regulatory Affairs, would sharply restrict the types of merchandise that street vendors can sell, limit their locations, require nonfood vendors to use wooden carts rather than tables, and increase the fees for licenses and bonds.