Ms. Adegoke jabbed a painted fingernail at the condo's billboard, which advertised apartments of $1.5 million and up.

He said the Fair Housing Office "may have to send its own people" to real-estate agencies "to find out where the apartments are" in cases where the agencies advertise apartments without providing specific addresses.

As a result, she said, the only way a broker can afford to advertise lower-priced apartments and still make money is to persuade the seller to pay a higher commission.

There are dozens of websites on which owners advertise their own private villas and apartments.

LEAD: Along the four-lane highway winding south from Tijuana to this Pacific Ocean resort town 65 miles south of the United States-Mexico border, new signs advertising villas, apartments and condominiums "Now Under Construction!"

Home prices are shooting up in the city, and in the last couple of years, local newspapers advertise apartments and villas costing more than $1 million.

It was there, during the recent revival of Williamsburg's Northside section, that artfully disheveled young residents posted thousands of fliers advertising apartments, announcing parties, selling furniture and seeking new drummers.

A placard on the front of the building during construction advertised apartments of up to seven rooms at annual rentals ranging from $1,500 to $2,000, marketed by Douglas Elliman & Company.

Frustrated brokers have to be warned repeatedly not to advertise illegal apartments using such terms as "mother-daughter unit," or "in-law apartment," said P. Gilbert Mercurio, executive vice president of the Westchester County Board of Realtors.

But they are telling just the same, like the changing languages found scribbled on sheets stuck on utility poles that advertise apartments and baby sitters.