Red, black and white "For Sale" and "Sold" signs are piled next to bulding plastic garbage bags out behind the largest real estate firm in this residential community across the Delaware River from Philadelphia.

The signs are stacked out of sight behind a fence because local realtors here say they are reluctant to buck anti-sign sentiment among residents.

It's only sentiment, not a local ordinance banning "For Sale" signs on residential property, that keeps them off the front lawns of 480 houses currently listed with real estate brokers in this community of 45,000.

Two weeks ago, the U.S. Supreme Court knocked down Willingboro's three-year-old sign ordinance. The court said such a ban - also adopted by communites such as Gary, Ind., Baltimore and Shaker Heights, Ohio, in an attempt to stop blockbusting and panic selling - violates First Amentment guarantees of free speech. But realtors here seem more concerned with maintaining a good public image than with exercising their constitutional rights.

"Realtors like to use signs in front of houses. It cuts expenses," said Stephen S. Tapper, president of March Realty Associates, the firm with its signs piled near the garbage bags. "I prefer putting them up in a community that doesn't mind the signs."

Willingboro does mind. The community has changed since it was created in 1959 by William J. Levitt, the developer of Levittown. Between 1970 and 1970, 3,000 black residents moved in and 2,000 whites moved out, raising the percentage of blacks here from 12 to 18 per cent. "For Sale" signs blossomed in some sections of town.

Deputy Mayor William J. Kearns, who helped introduce the ordinance, said some white residence were worried that their neighborhoods would end up largely black and began to "panic."

[One former resident of Willingboro, computer programmer Paul Chandler, who now works in Washington, maintains that there was no panic selling, however, Willingboro always had a high turnover of houses, he said. Cutbacks at neaby military bases and closings of large employment centers such as an RCA computer facility at Cherry Hill, N.J., added to the transiency of the area. In addition, Chandler charged, builder Levitt offered easy financing to customers, initially selling many of the $38,000 to $40,000 Willingboro houses "to people who couldn't afford them."]

But Keans said the community beganto stablize once the ordinance went into effect in 1974. The percentage of black residents has not increased, he pointed out.Home sales now result primarily because of job transfers, he said.

William Mellman, an area realtor who helped initiate the court challenge, agreed that the ordinance did stabilize the residential property market in Willingboro.

"We seem to be living in a more intelligent community now. The idea (of the ordinance) was not bad; it did get rid of several hit-and-run, irresponsible, realtors who were making money off the panic," Mellman said.

Mellman added that the ordinance was challenged because he and other realtors did not believe Willingboro had the right to stop realtors and private homeowners from communicating their desire to sell their houses.

But now that the realtors have the right to put up signs again, Mellman said they should be careful about how many they put up, keeping in mind that too many may hurt property values.

At March Realty, Tapper said that his company will be happy to go along with "the spirit as long as residential sales remain steady. Tapper, as well as several other realtors in Willingboro, said the ban had not affected his sales.

While local realtors have agreed to forego signs, a couple of homeowners and two outside real estate agencies had put up signs as of last week.

Rudy Ralff, who owns one of the firms, said he had a sign stuck in a lawn the day after the Supreme Court's decision.

"I just assumed all the other brokers would do the same thing," Ralff says. He says that about 30 per cent of his business is done with buyers who have found a house they want to buy because of seeing a "For Sale" sign.

"We get a very live buyer when somebody comes in here after seeing a sign. I would say that we are at least one-third of the way home on the sale," Ralff said.