For three years, Gordon H. Porter would return from vacation in Duck, N.C., on the picturesque Outer Banks, and dream, figure and plan how he could own a house there. Finally, this year, he found one he could afford: in a luxury community, for $49,000.

The house, 11 back from the ocean, has four bedrooms, 31/2 baths, a whirlpool tub in the master bathroom, and views of both the Atlantic Ocean and Currituck Sound. The community, Ships Watch, managed by a company to which Porter will pay $330 a month, has swimming pools for adults and kids, a hot tub, tennis courts and private beach. The monthly fee covers community association and management fees, as well as property taxes and homeowners insurance.

Porter's house could probably sell for 10 times what he is paying for it.

That's because Porter is one of 10 owners in a prepackaged partnership, a form of ownership that is being promoted increasingly around the country in high-priced vacation markets.

For his $49,000, the financial planner from York, Pa., will have the deed to a one-tenth interest in the property, and the right to stay there five weeks a year, with the dates shifting annually so that over time, all the owners get an equal chance at prime summer weeks.

In a market where vacation home prices have shot up at double-digit rates every year for the past few years, Porter knew that being a co-owner was his only way to own a house. Co-ownership, also called fractional ownership, is a form of timesharing. Promoters hate to use that word, though, because the reputation of the industry has been sullied over the decades by a history of sales frauds, as well as a reputation for high-pressure sales techniques and a weak resale market.

Co-ownership exacts a financial price beyond the cost to buy. Porter knows, for example, that his one-tenth ownership may or may not appreciate in value, although he's hopeful, and that it most likely won't keep up with the appreciation of single-owner houses. He knows that the way his house looks, inside and out, will be subject to the decisions of the other nine owners, whom he may or may not meet, and in some cases to review by the community as a whole -- especially now that the Ships Watch owners are assuming more decisions that the developer used to make.

And he won't experience the variety of renting a different place each summer. Instead, he'll be a landlord himself if he wants to rent the house out during his assigned weeks. Houses such as the one he is buying into typically rent for about $2,500 a week in June, July and August.

He's looking forward to staying in a house that he says is nicely furnished, with linens, beach towels and chairs supplied and the kitchen fully equipped by the management company. Porter's assigned weeks, for starters, are a week each in May and August, two weeks in November, and a week in February.

Porter, 47, has been vacationing in Duck for several years with his girlfriend, Lynn King, 44. When he first heard about co-ownership, "My first reaction, to be honest, was negative," he said. And he still has mixed feelings. On the one hand, he worries that he and King might get tired of the same property year in and year out. On the other, he said, "I don't know that a one-tenth interest is sufficient. I'd like to buy another segment."

Last year, Porter had assembled three other parties to go in on a $500,000 house and was just about to make an offer when two of them backed out. That arrangement would have cost $20,000 more a year per owner than the house could have rented for -- "to go to the beach a couple of times," Porter said.

Ships Watch is one of several developments on the Outer Banks where co-ownership is the rule, not the exception. There are also shared-ownership properties in resort towns in South Carolina, Colorado, Utah, Wyoming, California, Canada, Mexico, the Fiji Islands and the south of France.

One-tenth ownership sales in Duck this year have fetched $14,000 in a two-bedroom, 2 1/2-bath, townhouse-style unit and $59,000 in a four-bedroom, 2 1/2-bath detached house. Detached houses tend to command at least $40,000 for a one-tenth interest.

Financing for co-ownership purchases often comes from home equity loans against the buyer's primary home, local lenders said. "It's not something that you can walk in any bank or any lending institution and obtain a loan for," said Perry Byrum, mortgage loan officer at Wachovia in Southern Shores, just south of Duck. Other financing is usually arranged by a developer or seller, he said.

Wachovia, for instance, does not make loans specifically for co-ownership purchases, said Byrum, who was involved in such financing when his employer was First Union, which merged with Wachovia. Nor does Bank of America. "We don't finance things like that. We deal with property that you can own wholly," said Drew Wright, vice president at Bank of America in Kitty Hawk. Co-ownership interests cannot be expected to appreciate at the same rate as the overall vacation-home market, he said. "But when the market is tight, these things tend to catch up."

Ships Watch and Northpoint, another co-ownership community in Duck, have an arrangement with the Bank of Currituck in Corolla. The standard loan is for 80 percent of the purchase price, amortized over 10 or 15 years. Three years into the loan, however, it is subject to a "modification agreement," meaning it is refinanced at the prevailing interest rate over the remaining term, said Curtis Gauntt, branch manager.

Take a one-tenth ownership with a price of $62,500. The loan amount, $50,000, would be financed at 7.25 percent interest, Gauntt said. With a 15-year term, that means payments of $456.43 a month; over 10 years, monthly payments of $587.01.

The fees, Gauntt said, are a 1 percent loan origination fee and $350 for appraisal.

By comparison, someone buying the same house outright, for a purchase price of $625,000 and a loan amount of $500,000, could get a 30-year mortgage at a fixed rate of 6.5 percent, he said. Those payments would be $3,160 a month.

Neither calculation includes property taxes or insurance. Co-owners pay those in their management fee.

Judging from sales over the past three years in two co-ownership subdivisions in Duck, it is almost unheard of for people selling their interests to get bids for more than their asking price, as is fairly common in the fiercely competitive single-owner market. On the Outer Banks, houses near the ocean are routinely selling for $1 million or more, often to groups of people pooling their money as Porter originally wanted to do with his friends.

As escalating prices and shrinking supply squeeze people out of the single-owner market, Porter is optimistic about his chances for price appreciation. "The way I view it is that we made an investment in the equity of the property," he said. "There's more and more demand for this kind of second properties."

It would be a mistake to count on that, however, according to Tom Miller, legal counsel to the North Carolina Real Estate Commission, which regulates timeshares.

"Nobody should buy a timeshare with the idea that it will be a sound investment," said Miller, who emphasized that co-ownership is a form of timesharing, whether or not the real estate industry likes to call it that.

Since the passage of North Carolina's timeshare law in 1984, timeshares in general -- whether that means part ownership in a property or just the right to occupy it for a certain period of the year -- have been a fairly trouble-free industry, but the concept still has limits, Miller said.

"The same as applied 20 years ago still apply," he said. Buyers should:

* Understand that "this is the place they want to come to spend their vacation, not buy it with the idea that it will be a key into an exchange opportunity, because that's an iffier proposition."

* "Be wary of thinking that the timeshare form of vacation is going to be significantly cheaper" than renting a house every year.

* Be prepared for management fees to rise. Failure to pay the fees can result in a lien being placed on the owner's interest in the property. Higher fees have also been known to cause timeshare owners to abandon their interests, which "causes misery for the other owners."

* Anticipate difficulties reselling their co-ownership -- particularly if there are new properties on the market at the same time, if a co-owner has limited use of the house to show it, or if he or she has to travel a great distance. In some communities, the other co-owners have two weeks in which to buy an interest before it goes on the market.

* Make use of the legally required rescission period -- in North Carolina, five days -- during which a buyer can back out of a purchase without penalty. If a buyer has not read all the documents provided on the purchase, this is the time to do so.

With those caveats, Miller said, "We don't have any particular consumer problems. It's been years and years since we had to impose a fine" on a timeshare developer. Nor was the Consumer Protection Division of the state attorney general's office aware of any complaints about co-ownership, said spokeswoman Noelle Talley.

The National Association of Realtors has begun to take an interest in vacation home co-ownership. "We think that fractional ownership really makes a tremendous amount of sense," said Ben Blair, chairman of Coldwell Banker Griffith & Blair in Topeka, Kan., and vice chairman of the association's Resort Real Estate Committee.

Blair is testing the market, on a modest scale, in a single-family subdivision of 54 homes that he is developing in Grand Lake, Colo., near Rocky Mountain National Park. The model home is being offered in one-quarter shares for $162,000 each.

"A person can buy the right to occupy a million-dollar home for, let's say, $250,000 or $300,000" for a quarter-share, conveying up to 13 weeks of occupancy a year -- more time than most sole owners spend in a vacation home, he said. "The upkeep is all taken care of by the management company."

"It's a new concept to people, and it's just going to take some educating," he said.