EVEN AS THE WEATHER has switched so dramatically from hot to mild, it will inevitably turn to the bitter cold before public concern is stirred for the thousands of homeless people in this city--but what's so new about that? Here and there, make-do shelters are always open for the overnighters, who in the light of morning again disappear into the fabric of downtown. But now comes something different--an ambitious effort to do a little more. It is McKenna House, a project of the Washington Roman Catholic Archdiocese, and it deserves public attention and support as its doors prepare to open.

It is meant to be "more than a shelter," says Archbishop James A. Hickey, whose plans for the residence at 1501 Park Road NW are to provide vocational assistance, personal counseling, educational guidance and job and housing placement--"a home and a hope for the homeless." The Capuchin-Franciscan Friars, who will run the program, will work with various city agencies and volunteers to help those men accepted for roughly three-month residencies.

The project's planners note that this kind of help is geared to men who, in the opinion of the agencies referring them, are capable of living independently. (Religious affiliation will not be a factor in the selection). There are currently six more conventional temporary shelters under Catholic auspices in the area for men and women who need help.

The venture is a fitting tribute to the late Horace McKenna, a Jesuit priest who spent much of his life working with homeless, mostly black people, and who in 1970 helped establish SOME--So Others May Eat --which serves hot meals every day to many of Washington's poor. McKenna House will not look to the government for money, and so the public is being asked to contribute furnishings, kitchen and other equipment, appliances and, once the facility opens, clothing, job assistance and other volunteer help.

Nobody is expecting miracles from this project, but with offers of help received at 529-2188 and with the kind of commitment shown so far, project sponsors may find some new and encouraging responses.