Federal authorities have rejected California's proposed design for a driver's license for immigrants in the U.S. illegally, saying it is not distinguishable enough for security purposes from permits given to citizens.

The Washington officials want the license to state clearly on its face "that it is not acceptable for official federal purposes" and to have a design or color that differentiates it at a glance from other licenses.

The current design does not differ from other California licenses except for a subtle mark on the front and a disclaimer on the back in small print: "This card is not acceptable for official federal purposes."

Officials said Tuesday that the decision by the U.S. Department of Homeland Security could delay distribution of the first licenses because immigrant-rights activists have vowed to fight proposals that would make them look significantly different from other licenses.

The activists consider conspicuous markings to be a kind of scarlet letter. They and others say such marks could lead to mistreatment.

"Covering the fronts of licenses with this information that Homeland Security is demanding would subject the holders to unnecessary discrimination and possible harassment," said state Sen. Kevin De Leon (D-Los Angeles).

Leaders of the Latino Legislative Caucus called on California's congressional delegation Tuesday to demand that Homeland Security officials reconsider.

The decision "is disappointing and troubling," said a statement by Sen. Ricardo Lara (D-Bell Gardens) and Assemblyman Luis Alejo (D-Watsonville), the chairman and vice chairman, respectively, of the caucus.

"We strongly believe that the design submitted by California satisfies the intent of the law, by including a distinctive mark on the front, and the required statement on the surface of the license," they said.

They wrote to Homeland Security Secretary Jeh Johnson, asking him to allow the California design.

"As you know, immigrants are statistically more likely to be the victims of crime and are often primary targets for scams, discrimination, retaliation and extortion in encounters with a diverse set of unscrupulous actors," the lawmakers wrote.

For that reason, the California design is meant to provide "adequate protections for vulnerable community members from discrimination," they said. Approval of the California design, they argued, would be "confirming that DHS will not exploit the program for immigration enforcement purposes."

State Senate leader Darrell Steinberg (D-Sacramento) also sent an appeal to Johnson.

Meanwhile, the California Department of Motor Vehicles will go back to the drawing board, said Armando Botello, a spokesman for the agency.

"The DMV will continue to work vigorously with lawmakers, affected communities and federal officials to design a license that complies with federal law and allows over a million undocumented California residents to drive legally and safely on state roads," Botello said in a statement.

He refused to release a copy of the new license design.

Gov. Jerry Brown signed a measure last year allowing the DMV to provide driver's licenses by Jan. 1, 2015, to those in the country illegally. The governor said it would help people get to their jobs and schools and guarantee that they take a test to show that they are safe drivers.

In addition to the disclaimer on the back, the proposed license has the letters DP ("driving privilege") on the front instead of DL ("driver's license").

The Real ID Act approved by Congress in 2005 requires markings "to allow Federal officials to quickly determine whether a license or identification card may be acceptable for official purposes" including "accessing Federal facilities, boarding federally regulated commercial aircraft or entering nuclear power plants," according to the rejection letter.

The letter is dated May 1 and was released by the DMV on Tuesday.

State Sen. Joel Anderson (R-Alpine) said the state should take Washington's warning seriously.

"Clearly national security demands our state not assist in hiding people who reside here illegally," Anderson said.

patrick.mcgreevy@latimes.com