For the city fathers of Baca Raton, Fla., the news came as a shock.

Their application to the federal government for a community development block grant - that cornucopia of urban uplift money that buys parks and sewers and houses - was about to be rejected.

The U.S. Department of Housing and Urban Development's local office recommended turning down the application for one reason: It didn't promise any new housing for low-income families. And on the morning of May 25, the city was warned, top officials of HUD in Washington would concur in that denial and Boca Raton would be out more than $400,000.

On the night of May 24, the City Council convened and wrote in an agreement that Boca Raton needed 300 units of federally subsidized housing for poor families. Obligingly, HUD turned around the next morning and said Boca Raton's grant would be approved.

It was an illuminating illustration of HUD's new, increasingly controversial plan to pressure communities into offering subsidized housing for families too poor to afford the private market.

Many communities, particularly suburban ones, wants no part of subsidized housing, fearing it will bring poor people and their social problems into resentful middle-class neighborhoods. For some suburbs, it would mean opening the gates to blacks from nearby central cities.

Against that resistance, HUD has a $4-billion combination carrot and stick that originated in block grant legislation Congress passed in 1974.

Before that legislation, communities had to go to the government separately for each sewer or park or other development grant they wanted. Congress in 1974 lumped all these separate development programs together. Successful applicants are allowed to spend their lump sums as they please, provided they observe a few general federal guidelines. But one of these guidelines is the requirement that they provide low-income housing.

Some urban affairs experts regard this block grant as the government's most forceful tool for desegregating suburbs. It is openly acknowledged by HUD officials as a technique at to least for economic integration - to open up suburbs to the poor and moderate-income families long excluded by price of housing. "Dispersing" these families - using the leverage of the block grants - and thereby easing the strain on cities is a pronounced goal.

"This administration is much more a city administration' that the preceding one," said HUD Assistant Secretary Robert C. Embry Jr., who bosses the block grant program. "The previous one was elected by the suburbs."

Although it is yet to show concrete results, the new approach has delighted civil rights groups.

Andrew Mott of the Center for Community Change in Washington notes several examples of HUD turning back cities' applications because they lacked subsidized housing pledges. "There's a fantastic change in attitude on this," he said.

The key change, Mott and others say, came in April when HUD Secretary Patricia Roberts Harris issued instructions to local offices insisting that low-income housing be given priority in dispensing block grants. HUD officials were told to examine "past performances" of cities to see whether they were living up to housing promises made in previous' years' plans.

So far this year, one suburb - Hempstead, Long Island - saw its application for a block grant rejected because of what HUD deemed a "poor performance" on low-income housing. Several other applications, like Boca Raton's, have been approved only after changes were made.

Several suburbs - Warren, Mich., Cicero, Ill., Maple Shade, N.J. - stopped applying last year, apparently because they sensed the price of a federal block grant might be integrated housing. Parma, Ohio, abandoned its $4.5 million application last year rather than accede to HUD's insistence on a small number of low-income housing units. Haverford, Pa., didn't apply for one this year, having been told by HUD it had not considered its potential need for low-income housing.

The development block grants established by Congress in 1974 were part of the Republican administration's plan to give communities large blocks of money to use as they saw fit with few federal strings attached. One of the art's purposes, little noticed at the time, was "the reduction of the isolation of income groups within communities and geographical areas" and the "spatial deconcentration of housing opportunities of persons of lower income." That language is now cited by HUD as grounds for insisting on priority for low- and moderate-income housing.

Not much happened at first. The Ford administration chose not to enforce the housing requirements. And, with most low-income housing programs suspended under a moratorium declared in 1973, HUD had little money to offer as an inducement.

The attitude changed early in 1976 when the city of Hartford, Conn., successfully sued seven suburban jurisdictions and HUD, claiming they violated the law by not providing housing for poor people who worked in those communities but lived in Hartford. Federal courts ordered their block grants withheld. HUD responded with a new formula by which such communities would measure their housing needs when seeking block grants.

Now, with further refinement from the Carter administration, localities must estimate the housing needs of the poor who live within their boundaries. And in the potentially most explosive change, they must estimate the needs of those "expected to reside" in their communities. That phrase has been taken to mean low-income families that might move to suburban area to take jobs.

While some see this as potentially opening a big wedge into suburbia, others feel there may not be enough leverage in the block grant law to make a significant difference in living patterns.

HUD's Embry, for example, believes many suburban communities - perhaps a majority - will drop out of the program initially rather than risk local opposition to low-cost housing.Judging from recent talks with local leaders, Embry says, "At least a significant number will turn them down."

It is also questionable whether the amount of grant money involved is large enough to provide real leverage on suburbs, he said. Embry estimates that, on the average, the 80 big urban counties in the United States have only $4 million or $5 million at stake in block grants. For many of them that's not enough money to induce urban counties to go to the mate over low-income housing.

Embry is toying with other techniques to lure - or force - communities into the low-income housing field. One idea is to condition grants other than block grants on their housing performance. If threatened with a loss of such other federal programs as highways, FHA financing, and environmental programs, some communities might accept more housing for the poor, he believes.

Ultimately, he said, HUD may have to circumvent the suburban governments in this fashion: give money to central cities which would in turn finance nonprofit organizations which would buy or build low-income housing in suburbia for the benefit of poor city dwellers. That in turn might induce the suburban governments to do it themselves in order to get block grants.

"Then the county might say, 'Well, if it's going to happen anyway, we might as well do it ourselves and get [TEXT OMITTED FROM SOURCE]