The latest word in the Reagan administration's image-building campaign comes from Housing and Urban Development Secretary Samuel R. Pierce Jr., whose favorite words on fair housing are now on display in Washington's Metro stations, right up there with the cigarette and bank ads.

The message, a signed quote from Pierce, is displayed on bright blue signs in a half-dozen subway stations. It says: "Fair housing: I support it! The president sup- ports it! All America deserves it."

The administration, under fire from minority and low-income groups for what they view as a lack of commitment to civil rights goals and a lack of compassion in budgetary policies, has been trying to patch up its image of late.

Pierce, who, as the only black in the Cabinet, has borne much of the criticism, last week told a group of black Republican leaders he invited to Washington that the problem was one of "perception."

This particular corrective action was the brainchild of the National Association of Realtors, which is also footing the bill, according to HUD spokesman Leonard Burchman.

"The words are his," Burchman said. "He said it to them. He says that to everybody."

After test marketing in Washington, the association plans to take the ad campaign nationwide, Burchman said. Next target: Chicago, where Pierce's words will grace commuter trains and buses in the Loop.

"The secretary feels very strongly about fair housing," said Burchman. "He plans to make sure people know that."