To increase the country's increasingly short supply of rental units, Housing and Urban Development Secretary Moon Landrieu today proposed opening federally supported housing to all Americans regardless of income or wealth, provided they pay 25 percent of their income for rent.

At the same time he would give developers "whatever incentives are necessary" to produce rental units at market rates and "allow them to make a decent profit."

Landrieu stressed such a proposal is "not now public policy," but he added, "It is one that I am looking at and ultimately may choose to embrace." Landrieu launched the trial balloon at the American Bankers Association's 20th annual conference on Real Estate Finance, which is discussing prospects for the 1980s.

He conceded it would take some "rather radical changes" from past policy to treat housing as a necessity for all. the HUD policy has been to provide housing for low-income people. "Yet now we are finding that those who are above the median income levels are having difficuilty getting a home to buy or a place to rent," said the secretary.

Removing what Landrieu called "the artificial barrier of 80 percent" (of median income needed to qualify) would "take the stigma off what is generally considered to be public housing today," he said. When the government first began subsidizing housing in the 1930s, it built units in good locations he recalled. "Today we condemn people when we put them in housing that is stigmatized as housing for the poor," the secretary added.

This approach also would eliminate the resentment of middle-income Americans who aren't eligible for government-assisted housing and must pay higher rents elsewhere, he explained.

Landrieu also said HUD is debating whether to stop setting market rates on FHA-insured projects. "I think we are ultimately going to wind up giving some kind of incentive to the private sector to build -- whether through interest-rate reduction or some device we haven't thought of yet -- and let the marketplace fix the rents," the secretary said.

Landrieu, who was mayor of New Orleans and also involved in real estate before he became HUD secretary six months ago, indicated his ideas face considerable opposition from his subordinates who tell him they haven't worked before and won't work now.

In his desire to "re-examine everything at HUD," Landrieu has appointed a committee of 35 to look at choices for HUD in the 1980s. The group, consisting of public officials and prominent developers who specialize in renovating downtown areas, is expected to make recommendations with the year.

Some topics for discussion include eliminating unnecessary regulations and building requirements, constructing smaller but better housing and developing new financing methods. Among the possibilities mentioned were tax-exempt, mortgage-backed securities, as well as graduated payments and rollover mortgages.

In the near term, the secretary offered little new in the way of aid for the recession-plagued housing industry. "We have resisted massive salvage programs, much to the unhappiness of some," he said. "In my judgement it's not time yet, although there may come a period when it has to be done."

The Carter administration last month announced support for limited assistance, far short of what the industry requested. Landrieu said Congress appears to be dragging its feet on approving interest-rate subsidies on FHA loans to middle-income homebuyers. This plan would enable households with incomes of up to $27,000 to obtain mortgages of up to $60,000 at 11 percent interest. But once the legislation passes, HUD will have the program in action 30 days later, he added.

Lee E. Gunderson, the ABA's president-elect, urged bankers to use the "incredible array of new tools that have recently come into our hands" (as the result of bank deregulation legislation) to increase their capital for mortgage lending.

To fight competition from money market mutual funds, which are draining deposits, he said the ABA has created a "money market fund strike force, with the aim of leveling the most lopsided playing field that banking has ever faced." It will fight for government regulation of the funds.

Another part of the banks' competitive strategy is to develop new savings instruments with yields equivalent to those of money market funds by pooling deposits to form large certificates of deposit and comingling agency accounts for bank trust departments.