Morton D. Weiss has an idea for a "brain trust" of retired workers to help communities across the nation at a cost "of peanuts."

It's his way of easing two of America's big problems: the spiraling cost of government and the sense among many retirees that "like Old Dobbin, they've been put out to pasture."

Weiss, who is 75, retired 15 years ago as a management analyst in the federal government. A few years ago -- after watching what was happening to other retirees -- he established a "human resources" organization he calls Mobilizing Mature Manpower, amid in part, at keeping retired workers "in the mainstream."

Many retirees, he says, "who have been active all their lives," after leaving their jobs "withdraw from life." All too soon "they end up in Gawlwer's" (a funeral home).

"Too many of my contemporaries just fall apart. They say, 'My memory is going.' We've got to work at life."

Weiss operates out of a cluttered office he shares in the National Press Building. On the wall is a pay telephone. It makes it easier, he explains, to let others use his office when he's away.

So far, his organization is only in the talking stages. He has briefed a number of officials and gotten some press publicity in his vacation travels around the country. In 1977, Sen. Charles Percy (R-Ill.) inserted a favorable mention in the Congressional Record.

What he envisions is "informal" groupings of the perhaps 12 retired men and women -- lawyers, accountants, economists, doctors, managers, business exectuives, bureaucrats, scientists -- who would donate their talents to help solve municipal problems.

It would be, he says, " a research arm for any adminsitration wanting to take advantage of its talents. There are enough problems in this city every day that could keep dozens of groups in the metropolian area busy."

It's the kind of consulting help, he says, that otherwise might cost a city "a couple of hundred thousand."

Such problems could include "street conditions, the need for better fire protection, the need for security on streets and buildings."

These groups, provided with inexpensive office space, could meet regularly to discuss projects they might want to tackle."the interchange of ideas," he says, could lead to solutions.

Weiss spends about 30 hours a week promoting his idea. "It's kept me agile, alive and interested.

"I'm pushing just as hard as I can. My contemporaries and I must leave a better legacy than we appear to be leaving -- a helluva mess."