Interval ownership, a new concept in lodging that combines the amenities of a hotel with the benefits of condominium ownership, will soon be available in Washington.

The Barclay House, which is scheduled to open in October in the West End, offers the opportunity to buy and sell specific time units in the 26-suite building, ensuring peripatetic businessmen or frequent visitors to Washington a comfortable place to stay. ccording to Jim Locke, president of Barclay Properties Inc., it's a concept whose time has come.

"We expanded it and adapted it to an urban environment," Locke says.

When the $3.5 million Barclay House is finished in October, it will contain 26 almost identical one-bedroom suites, each with a fireplace, a wet bar, a fully equipped kitchen and remote control Home Box Office. Barclay is spending about $45,000 per apartment for decoration.

To own an interval is to own in perpetuity a block of seven days that can be used anytime during the year and in any configuration. Locke emphasizes the flexibility of the plan. If an owner is unable to get a suite on a particular day, Barclay will find a room at a comparable area hotel and pay $100 toward the hotel bill. Owners who find themselves in such a situation retain that day's credit.

In order to avoid scheduling conflicts Barclay will sell only 50 weeks or intervals for each unit, which means that 52 intervals or the equivalent of one extra suite will be made available.

Initially, one interval will be priced at $8,500, but Locke expects that figure to be $13,750 by December 1982. Barclay has already sold 200 intervals and expects to sell all 1,300 by next year. Fifty percent of the purchasers have been businesses and the other half individuals.

Once inside the Barclay, the purchaser can take advantage of such features as daily maid service, free valet parking, 24-hour switchboard, limousine, secretarial and clerical services. Barclay is currently interviewing candidates to serve as a concierge. Owners are assessed an annual maintenance fee of $350.

Individuals may sell their intervals, but Locke cautions that the Barclay should not be viewed as an investment. Barclay Properties will not be involved in any reselling of intervals, but will circulate a newsletter with the names of potential buyers.

Through an affiliation between Barclay and Resorts Condominiums International, which has more than 500 resorts worldwide, owners may also swap their intervals for similar lodgings throughout the United States, Europe, South America and Japan.

Barclay had the consulting firm of Laventhal and Horwath perform some statistical analyses of interval ownership, including pay-back time. For businessmen who travel often and normally stay in hotels, the pay-back period is anywhere from two to five years.