BLAME THE cloudy weather or our need for new steak knives or the lure of getting in on the hottest real estate innovation since the condominium. But the fact is, last October my husband and I walked into an Orlando shopping mall to buy some inexpensive souvenirs and wound up spending $11,300 for a two-week deed to a Florida time-share resort.

Time-sharing is an increasingly popular plan by which developers sell resort property in increments of a week or more to a number of buyers. Marketed under titles such as "interval ownership," "right-to-use" and "club membership," it is -- claim industry experts -- the fastest growing segment of the real estate market.

Since its introduction to the United States from Europe in the early 1970s, time-sharing has been touted with great success as an affordable way for inflation-crunched families to own vacation property. Time-share sales have nearly doubled every year since 1975, says a Federal Trade Commission report, with 1980 sales exceeding $1 billion.

There are currently more than 800 U.S. time-share resorts in more than half of the states -- up from eight in 1973 -- according to the National TimeSharing Counsel. The greatest number are in Hawaii, Florida, California, Colorado, South Carolina and Texas. Many of these resorts belong to exchange clubs, which allow their members to swap their unit-time with other owners in the United States or in the more than 200 international time-share resorts.

And on that cloudy fall day, my husband and I became one of the estimated 350,000 families to board the time-share bandwagon. Neither of us was familiar with time-sharing, nor were we in the market for a vacation home. We were simply visiting Disneyworld for a week, spending a sunless day shopping.

But when we approached what we thought was an information booth in the mall (to ask about mailing gifts home) a bubbly blond launched a fascinating spiel about "a great, new inexpensive way to buy into a Florida resort and trade it for space in vacation spots around the world."

Intrigued and slightly amused, we signed up to tour Vistana Resort the next morning. It would be, we thought, a lark. Two cynical, tough customers like us, we assumed, would find the catch in this "too good to be true" scheme and refuse to buy.

Twenty-four hours, $11,300 and a "free" knife set later (our gift for taking the tour), we were the somewhat trepidatious owners of two weeks at Vistana.

Our "Vistana morning" began when a minibus picked us up at our hotel and took us to the resort sales office. We were ushered into a brightly lit room where about 2 dozen other prospective buyers were gathered, munching donuts and drinking orange juice. Each family was assigned a sales representative -- ours was Karen Eld -- and a table. After some small talk, we were shown a film starring George Kennedy that highlighted the benefits of time-sharing.

The major point stressed repeatedly was time-sharing's "inflation-proof" quality. For a one-time purchase price (which they held off mentuioning until the very end of the sales pitch), a Vistana owner purchased one or more weeks which could be used, exchanged, sold, rented or willed to beneficiaries.

"Resort rental costs are currently rising by 10 to 15 percent and more each year," reads the sales brochure. "The one-time Vistana purchase price, excluding maintenance fees, guarantees you will have a resort vacation every year . . . you can fix your vacation costs for life for less than it would cost to buy a new family car."

After the film, we bombarded Eld with questions. First, and most obvious was how much? Cost varied according to two major criteria: Season selected -- low, medium or high -- and size of the accommodation -- a villa sleeping six or a townhouse sleeping eight. The per-week price for a villa in medium season was $5,650 -- including settlement costs.

That seemed reasonable, so we continued grilling. How did the exchange program work? Vistana is associated with Resorts Condominium International (RCI), Eld told us, the country's oldest and largest time-share exchange network with more than 650 resorts in more than 30 countries around the world. Our first year RCI membership would be included in the purchase price, after which it would cost $42 per year to belong, plus $38 for each week exchanged successfully.

To exchange, members "deposit" their own vacation time in the "RCI Spacebank" then "make a withdrawal" by filling out a special form requesting a vacation in a different RCI resort. (They suggest you list several resorts, in case the computer can't match you with your top choice.) Spacebank deposits must be made at least 60 days prior to the vacation time, and RCI had to receive the exchange request form at least 45 days prior to the time requested for domestic exchanges, 60 days for international exchanges.

You could only trade within your own time period (high, medium or low season) or to a less-desired time period. That meant the owner of "high" season time could trade for any time period, but someone who owned in "low" season could not trade up to medium or high.

Exchanges weren't guaranteed, Eld admitted. We might request a swap with a resort in Japan or Israel and not match. But she stressed that RCI figures show 90.8 percent of properly submitted exchange requests are successful. And the key to successful matching, she assured us, is buying in a highly requested resort. Since Orlando is one of the two most requested exchange locations (Hawaii is also popular), she claimed we should have no trouble matching.

"What if we can't use our time one year?" we asked. We could let friends or relatives use it, rent it ourselves or have the company rent it for $120 per day (for which they charge a 35 percent fee). Or we could "bank our space" with RCI to use the next year. "What if we couldn't use our time during the specific two weeks we purchased?" We could process an exchange through RCI to switch for other weeks at Vistana or at another resort.

Among her other answers to our many questions: Only 51 weeks were sold in each unit, leaving one week for maintenance. We were insured for everything from bodily injury to sinkholes. There was midweek maid service (also available daily for a small fee), security staff, controlled guard gate and complimentary shuttle bus service for the five-minute drive to Disneyworld.

When we'd run out of questions Eld drove us to the resort, which consisted of 98 units in 11 buildings and a recreation area containing tennis courts, a swimming pool, jacuzzi, clubhouse and jogging track. The villas were lovely: two bedrooms, two baths, living room with pull-out sofabed, dining room, breakfast bar, television, telephone with 24-hour answering service and fully equipped kitchen -- everything from dishwasher to clothes washer and dryer.

By this time, our resistance had nearly faded, and both of us were almost ready to sing. Neither of us were wild about spending two weeks a year in Orlando, but were basically interested in the exchange option. We realized there was some risk to this approach, since exchanes aren't guaranteed, but decided to gamble.

Eld took us into a salesroom that was buzzing with the sound of other couples poring over deeds and credit cards clicking imprints onto sales receipts. We looked over a huge grid of exactly which weeks were available and chose one week in June and one week in December, both in the "medium" time/price range but adjacent to the "high" season. We were told that, since Orlando tourism was booming with the imminent opening of Disney's Epcot center in October 1982, and the construction of other projects such as "Little England," our medium season might be converted to high season at no charge to us.

Since time-share purchase, like any real estate transaction, is subject to state law, we discovered Florida a good place to buy. Laws are relatively strict -- probably as a result of past "swamp land" sales fiascos -- and included provision of a 15-day "cooling-off" period during which we could cancel without obligation.

Buoyed by this escape clause, we used our American Express card to make a 25 percent down payment ($3,250), which left us with an $8,050 mortgage to be paid off at 15 percent interest -- for a total of 84 monthly payments of $155.36. (And interest on finance payments, of course, is tax deductible.) Our yearly maintenance fee -- which is subject to increase -- is $326 ($163 per week).

The whole process took about 3 1/2 hours.

When we returned to Washington we researched time-sharing and discovered numerous articles describing the benefits and hazards of the plan. There were some horror stories of resorts cited by the FTC for deceptive and misleadng sales practices. There were sad tales of people who bought in the Poconos, assured they'd get an exchange in Paris only to find that wasn't so.

(Recently, the company attempting to sell the first time-sharing property in the District -- Barclay House near Washington Circle -- filed for bankruptcy, blaming the slow real estate market and the lender's failure to release agreed-upon funds. This attempt at "urban time-sharing," directed at business customers, is a new twist to the resort time-share concept, notes Randall Scott, executive director and counsel of the National TimeSharing Council.

("There are only a handful of urban time-sharing projects in operation right now," he says, "and they must be very well conceptualized to work." He declind to discuss specifics of the Barclay project since it is in litigation, but noted "we're highly distressed that a project in Washington didn't work out. It has a tendency, needlessly, to leave a bad impression in people's minds.")

As we told friends and relative what we'd done, we discovered other owners in our offices and exchanged details of our various plans. We found that there are two major types of time-sharing plans -- deeded, like Vistana, where you buy an ownership interest in a piece of real estate, and nondeeded, where you buy a lease, license or club membership which lets you use the property for a specific amount of time each year for a stated number of years (typically 12 to 40).

One colleague who owned nondeeded time-share property in Majorca said she'd been very satisfied with the arrangement. Relatives who owned deeded time-share property on the west coast of Florida were also happy. This psoitive feedback reassured us we hadn't been totally ripped off in a moment of temporary insanity.

Among the other time-share facts we uncovered from the National TimeSharing Council:

* "Average" time-share purchases are well-educated, middle-aged couples with one or two children living at home, with a median income of $37,500.

* The average number of weeks purchased is 1.6.

* Units range in price from about $1,500 to $19,000 per week, depending on size and decor, location and season.

* The average unit price in 1981 was $6,051 per week, with a $152 maintenance fee.

* More than two-thirds of buyers finance their purchases, with average down payment of 15.7 percent and average loan payback period six years. Interest rates vary according to the prime rate.

* Other exchange networks include the six-year-old Interval International with more than 300 resorts in 35 countries, and Network One, a four-month-old company with about 20 resorts around the world.

After studying the subject and reading the expert's advice on what to do before you buy, we decided Vistana measured up. So we decided not to invoke the escape clause. The real test, we felt, would be our exchanges.

The first -- and only one -- we've taken so far was from May 21 to June 4. We started planning in February, since we had to "deposit" our time in the "space bank" 60 days before our vacation time. Then we leafed through the RCI "dream book," looking for a suitable spot to "make a withdrawal." Since we both loved the sun and ocean, and wanted to hold down airfare costs, we picked resorts in the Bahamas.

But we had a few questions about the resorts, so we tried to call RCI's toll-free number for more information. After three days of frustration -- getting nothing but busy signals -- my husband finally reached RCI and was told to call early in the morning for the best chance of getting through. Then, when the RCI clerk called up our account on their computer, she said Vistana owners were not eligible to trade until June.

Angered, my husband called Vistana, where a customer service representative assured him RCI had made a mistake that she would remedy. Several hours later she called him back to say that the problem was resolved. We checked back with RCI to make sure and were told to go ahead and send in our exchange request. On the request form, we listed nine resorts whose location and accommodations seemed good. In March we got a phone call from RCI, informing us that we'd matched with our fifth choice, Club Land'or on Paradise Island.

The reason we hadn't matched with one of our first choices, we were told, is that it was difficult to match two back-to-back weeks as we requested. Did we want to confirm? We said yes.

A few weeks later we received a confirmation notice and cheery packet of material from Club Land'or describing the facilities and the island. They included several helpful hints, including the suggestion that we buy groceries in Nassau on our way over to Paradise -- which is connected to the Bahamas' capital by a bridge.

From the moment we arrived, shortly after the 3 p.m. Friday check-in time, everything went smoothly. Our room was much smaller than at Vistana -- one bedroom, one bath, small kitchen and living room -- but it was plenty of room for the two of us, and we'd been told about the size in advance. There was no dishwasher -- but the maid who cleaned the room daily washed the dishes. The five-year-old club bordered a picturesque lagoon, had a small swimming pool and was a short walk from several lovely beaches. By renting bicycles ($8 per day) or motorscooters ($22 per day), we could get to several nearly deserted beaches that had soft white sand and excellent snorkeling.

Most of the other vacationers were owners returning for their yearly vacation (only about 18 percent of us were on RCI exchanges), and many were already old friends from past visits. As it turned out, about 90 percent of Land'or owners were Washington-area residents, since the club sales offices is based in Virginia.

At a welcoming poolside cocktail party, complimentary "Bahama Mamas" were served and Smitty -- the social host -- told us "There are three speeds in the Bahamas: Slow, stop and reverse." He outlined the week's activities, of which we attended two: a boat ride to a nearby deserted island where they served a barbecue dinner and all the alcoholic beverages you could drink ($40 per person), and a luncheon featuring native conch dishes ($6).

One highlight of our "trip to Paradise" was parasailing, which is similiar to parachuting but doesn't require jumping from a plane. Instead, you start on a raft in the ocean and are pulled into the air by a motorboat. The boat sails you around over the water for about five minutes for a $20 fee. Other delights included Nassau's botanical gardens and native straw market, trying several new fruits -- including soursop, which tastes like a mango crossed with a coconut, the cabaret shows at the new Paradise Island Casino, wonderful shelling at the less-frequented beaches and plenty of fresh grouper and conch.

At check-out time, after two weeks, our total bill was $82 -- the cost of the boat ride and luncheon. The club staff had made reservations at shows and restaurants for us and been exceedingly helpful, without any charge.

Next year we may spend one week at Vistana, to see Disney's new Epcot center. Or we may try an exchange in Israel. Or Spain. Or Japan. There are no guarantees. But so far, so good.