The focus is on home repairs at Chicago's City House Exposition

Landlord-tenant relationships are usually as good, or as bad, as each party's clear understanding of mutual responsibilities. It is an understanding that should be spelled out in writing, according to Jack Kaplan, an attorney who took part in panel discussions at the recent sixth annual City House Exposition here.

More than 25,000 house and apartment owners talked with hundreds of exhibitors and asked questions of panelists at this year's fair, which continued the trend to focus on practical home repairs (large and small), shifting from the fair's original emphasis on restoration.

Members of panels discussed borrowing to weatherize, furniture refinishing, gardening tips, consumer justice, energy loans, and restoration of architectural detail.

Landlord-tenant panelist Ken Williams, housing coordinator for Access Living, a handicapped-citizens advocacy-action organization, pointed out that ''disabled people on fixed incomes have little choice in housing agreements, particularly the hearing-impaired.'' He urged landlords to be more sensitive to their handicapped tenants.

According to panelist and Chicago Alderman David Orr, Chicago ''is the most anti-tenant of the nation's major cities,'' lagging far behind other cities in legal protection for tenants. Mr. Orr urged adoption of his 10-point ''tenant bill of rights,'' which he said also protected ''responsible landlords.''

Ordinances in the bill provide the right to repair and deduct from rent, a fair lease and the right to break a lease if an apartment is not maintained, protection from unfair eviction, a security deposit limited to 11/2 months rent, and protection from a landlord's unreasonable ac-cess.

The bill must pass the city's building committee and the City Council; its success, Mr. Orr says, depends on ''a strong tenant outcry.''

Panelists agreed that security deposits should equal no more than a month and a half rent. If damages were greater than the deposit, they told a dissenting landlord in the audience, he could bring suit to recover the loss.

Bill Gunderson, director of the Chicago Housing Department's fair housing division, advocated a uniform screening process for tenants ''to eliminate most problems later.''

Other activities at the fair included demonstrations by apprentices from Washburne Trade School of house crafts such as painting, carpentry, carpet laying, upholstering, and plastering. One booth promoted the talents of women trade apprentices from the Sunbow Foundation.

Among the commercial fair exhibits was Barclay Products, manufacturer of bathtub and sink reproductions of the late-Victorian era, and of brass plumbing fixtures. A popular item with younger customers ''who are rediscovering yesterday's traditions,'' says owner Connie Raffel, is a handsome $800 claw-and-ball-foot red plastic tub.''

Exhibitor Nancy Hubby came from Philadelphia to sell her book, ''Preserving and Maintaining the Older Home,'' written with Shirley Hanson. As professional city planners and preservationists in Philadelphia's Chestnut Hill historic district, the authors teamed up five years ago to write a book with practical, easily understood advice on old-house repair.

In 1976 Mrs. Hubby wrote a conservation manual for a Detroit neighborhood group. Encouraged to expand the manual, she added photographs. ''We thought we'd finish the book in a year but spent four years researching and writing, plus another year with McGraw-Hill for publication,'' Mrs. Hubby said.

Fair headliners included Bob Vila of ''This Old House''; Jeff Smith, host of ''The Frugal Gourmet''; ''Victory Garden'' star Bob Thomson; and Beverly DeJulio , ''Mrs. Fix-It'' of Chicago radio and television.

While some visitors managed to resist the blandishments of solar room additions, roomy kitchen cabinets, art glass, electronic security systems, energy-saving furnaces, and how-to-do-it books, one fairgoer admitted he did not leave the four-day fair empty-handed, succumbing to a lightweight heat gun ($59. 95) to speed the stripping of Victorian house woodwork.