Because he wants to make their lives and those of their families "as pleasant and comfortable as possible," Mayor Marion Barry has asked all members of Congress who live in the District of Columbia to send him their names and addresses.

In a letter sent recently to every lawmaker, concluding "with warmest personal regards," Barry said he wanted the information "for the use of executive branch agencies." He offered no explanation how he could improve their comfort.

Barbara C. Washington, an assistant city administrator who serves as Barry's chief lobbyist on Capitol Hill, said the mayor wants "to do what we can do to make certain that members of Congress do not have to go through what is considered the bureaucratic maze" in dealing with municipal problems.

For example, she said, city agencies will check the congressional list to assure that water service is not cut off or cars booted for unpaid tickets without first telephoning the lawmakers as a courtesy and giving them a warning. She said "30 or 40" congressmen have responded to the letter.

Even one of the city's best congressional friends, Rep. Stewart B. McKinney (R-Conn.), has complained of congenital foul-ups of water bills. In one instance he cited, a House member was unable to sell his house because the city could not find a three-year-old bill that had gone astray. Solving that required personal intervention by City Administrator Elijah B. Rogers.

Responding to a reporter's question, Washington said the letter to congressmen doesn't mean some city residents are more equal than others. But, she said, with Congress still the final arbiter of the city's laws and finances, "we must deal with the realities of life in D.C."