Some housing observers had detected a slight slowdown in new home-buying in this region during the mugginess of July and August. But recently there have been a few instances of a buying mania more characteristic of Southern California.

Would you believe that one prospective buyer in the Baltimore area parked a rented recreation vehicle on the site of some uncompleted town houses a week before deposits were to be taken? The Chapel Ridge dwellings are in the new community of Mays Chapel Village, just north of the Baltimore beltway and due west of the Timonium fairgrounds.

"It really happened," recalled builder Lee Rosenberg. "Mike Daughterty, his wife or one of their relatives maintained the buying vigil for a full week to be first in line and first to make a choise of model and location." Rosenberg is a partner with Seymour Raphael in the Columbia-based Howard Homes, Inc.

"In the week before we took deposits there were 11 families camped on the site and they made their own line and guide lines for waiting. They even posted rules. There were half a dozen campers, plus cars in which people slept," Rosenberg said.

Why such an urge to buy?

"It's simple a matter of location, product and price," the builder said. "First, the location is close to Baltimore and the beltway and the new community being developed by James Kielty & Co. is a beautiful 350-acre tract in an area that is attractive to many persons. The site also is near the Baltimore Country Club."

As to the product, Rosenberg said that Howard Homes is building traditional, all-brick town houses with three bedrooms and two-and-one-half baths. He added that the basic dwellings have 2,200 square feet of living space and are priced from about $47,600. (Fireplaces and balconies are options.) That's about $22 a square foot, well below most new and redone town houses in this area.

The interest in the Chapel Ridge town houses was such that the builders had a list of 675 names in mid-September to which brochures were mailed on Sept. 21. In July, after ground was broken, there was no sign or promoiton on the site until visitors and callers asked for information, Rosenberg said.

"In August, James Kielty IV suggested that we put up a sign to take off some of the pressure of calls at Mays Chapel Village," said Rosenberg. "So we put up a 2-by-3-foot sign with our name and telephone number. And then we began taking names at the office and telling people they could see our somewhat similar Elkhorn Landing town houses in Columbia."

On Saturday, Sept. 24, 97 deposits of $500 were taken at Chapel Ridge, where only the first 59 town houses were put on sale. Now deposits have been taken on nearly all of the 170 units planned in the first two sections. Settlements are expected to begin in late November and continue through next year.

Howard Homes has land for 230 town houses but may buy more because of the terrific response, Rosenberg said.

While the response to this development north of Baltimore was unusual, a few Washington area builders and developers also have been selling strongly in recent months.

For instance, the Normandy Falls single- family houses in Potomac - which range in price from $130,000 to $170,000 - have been sold from a waiting list for two years. Earlier this year, the developer, C.I./Mitchell & Best Co., began developing houses and 75 town houses at Tuckerman Lane and Falls Road.

"We started with a list of interested families in March and had nearly 300 names by the time we were ready to offer the first 14 houses in early September," said Kenneth D. Grunst, sales manager. Appointments were set up on a priority basis, beginning at 9 a.m. on Sept. 10 and by 2 p.m. all 14 available houses were sold.

"The average price was $120,000, Grunst said. "By Sunday evening we also had 52 back-up deposits of $300. That deposit is merely to hold the house a week or 10 days before a contract is signed and 3 per cent of the purchase price is paid."

The foundations of the houses were barely in place but prospective buyers inspected sites and looked at floor plans and full descriptions of the houses. Sales manager Grunst, who has sold about $26 million in new houses in Potomac in eight years, said: "I've never witnessed a market or experienced a response to a group of houses anything at all like we've seen this year."

Partner Robert L. Mitchell added that the firm also is experimenting with a new farmhouse model. One has been built and sold at 5 Sprinklewood Ct. in Potomac.

"Actually, this house has one of our standard floor plans inside but the exterior, as designed by Patterson & Worland, is so farmhousey that my youngsters insist it is just like the Walton homestead on TV. It's really a 1977 house with the face of a house built several generations ago," he said.

Elsewhere in Potomac, Kettler Brothers has accumulated some 600 names of people interested in buying single-family houses at the yet-unopened North Farm community adjacent to Woodmont Country Club on Montrose Road, east of Route 270. Prices will start at about $112,500.

Carl M. Freeman Associates has 280 persons listed as interested in the brick town houses that it plans to introduce soon on a wooded site near Cabin John Park and Seven Locks Road. Prices will begin at $85,000, according to executive vice president Norman Dreyfuss.

The contemporary house market in Potomac has been strong for Berger-Berman Builders, which as been selling its $125,000 houses at the newly opened Potomac Springs development ahead of completions.

"We could sell more if we had the lots and capacity to deliver," said partner Peter Berman.

In Northern Virginia, Centex Corp. accumulated a big list of prospective buyers for its $125,000-range single-family houses in Langley Oaks, which is inside the beltway in the McLean area. In the under-$100,000 market, houses at the Twin Lakes and Woodberry developments have been strong sellers in the new Burke Center community in southern Fairfax County.

Another strong-selling entry in the area housing market is the Southampton town house community undertaken by Richmarr Construction Corp. in the Pentagon City area of south Arlington. The site is near a Metro station and across Route I-395 from the Pentagon. Almost all of the first section of 96 upper-price-range, stacked town houses have sales deposits well ahead of completion, according to a Richmarr executive.

In Bethesda, the Holladay Corp. has bought and remodeled a section of the generation-old Bradley Boulevard apartments in Bethesda. A spokesman indicated that the completely rebuilt town houses have sold out - without benefit of advertising - at prices from about $68,000 to $110,000. In one eight-day period, 116 deposits of $500 were taken. The first section includes only 42 dwellings.

Continued vibrancy in the residential market place will depend, as usual, on availability of mortgage funds. That money has been generally in good supply most of this year, although interest rates have inched up in recent months.

Some Washington area builders report that buyer response this year has exceeded realistic goals. However, a dimunition in "looking traffic" has been noted in recent weeks, causing some concern to marketing executives who are fretting that the desire or capability to buy might be slackening. Of course, the slowed traffic in house shoppers might be explained by two rainy weekends and diverting "Redskin Sundays."