Washington's new housing director, James E. Clay, is reshuffling his department and reviving some old-fashioned policies in an effort to improve a decaying stock of nearly 12,000 public housing units and collect some of the millions of dollars owed the city in unpaid rent.

Reversing a five-year-old trend toward centralized management of public housing, Clay last week placed property managers on site at most of the city's 52 housing projects and gave the managers responsibility for collecting rents, which are are supposed to total $14.3 million in this fiscal year.

"We're going back to basics," said Clay, who recently returned to Washington after a year as director of the Kansas City, Mo. public housing authority. "We're going back to some of the simple things we know need to be done. We have attempted some flashy things and gotten away from the basics."

Last May the General Accounting Office, the investigative arm of Congress, reported that Washington had failed to collect as much as $3.3 million in unpaid public housing rents because the city had no reliable way of verifying who had paid.

By last December 5,895 families, or nearly half of all the families living in public housing, owed the department a total of $3.6 million in unpaid rent, according to housing officials.

The city has tried at least three different collection agencies during the past several years in its efforts to remedy problems with rent collection. Until last week, tenants were mailing their rent payments to a collection agency based in Baltimore.

Clay said that it took 45 days under that system to determine whether a tenant had paid. With resident managers collecting rents, he said, "if they have not paid by the fifth of the month, the manager can start knocking on doors and by the tenth can make a report" to the public housing administration for further action.

In recent years, managers have been responsible for a number of projects. Under the new system, each will generally be responsible for only one major project, although a few smaller projects still will be handled as a group or together with a larger project.

To implement the new system, Clay has added 17 new managers to the department's existing staff of 23. Four of the new managers are tenants. Four projects are privately managed.

The city government is the landlord for almost a tenth of Washington's population. Much of the housing it provides is among the worst in the city and is occupied mainly by single mothers with two to three children, who receive public assistance, and by elderly women who receive small Social Security payments.

Mayor Mayor Barry repeatedly has promised to improve public housing since taking office in 1978, but thus far has met with little visible success.

Clay told a general staff meeting two days after he took over the department that improving public housing would be his top priority.

Almost immediately he shook up the department by reassigning 17 employes, including some mid-level professionals, to work on public housing.

They were assigned to try to reduce the massive waiting list of families seeking public housing and to attack a year-old backlog of reviews of tenants' income, done routinely to determine whether rent, which is calculated as a percentage of a resident's income, should be increased for any tenants.

Last week, Clay said publicly for the first time that he intends to replace all of the department's administrators, whom he helped select four years ago when he was the department's deputy director.

"I want my own team in place," he said.

Administrators James Woolfork and Marcus Dasher and acting administrator Carrie McHenry already have left the department.

McHenry will take a job with the city's new department of Consumer and Regulatory Affairs, which has taken over some functions formerly performed by the housing department. About one-fifth of the housing department's staff have been transferred to the new department.

The remaining administrators include: Sidney Glee, public housing; Kenneth Colburn, policy and planning, and James Kerr, development.