In five years of playing cupid via videotape, Georgetown Connection founder Joan Hendrickson has become closely acquainted with the special concerns of Washington singles.

"Loneliness is the biggest problem," says the 49-year-old matchmaker, who is separated and has three grown daughters. "People moving around with their careers often find it hard to meet compatible others. Singles also have special needs in terms of things like finances and insurance, and there are areas where single people are slighted, like travel."

With "unmarrieds" accounting for nearly half of all Washington area households -- and one out of three adult Americans -- "singles could be an important economic, political and social force," she asserts, "if they got together to identify their common needs and concerns."

For the past nine months Hendrickson has been working to do just that by coordinating "The First National Singles EXPO," which she hopes will bring 10,000 singles from around the country to the District next August.

"We're planning 2 1/2 days of lectures, workshops and seminars, all dealing with issues of singleness -- like single parenting, coping with loneliness, the older single, 'single-nomics.' There'll be an exhibit hall display of products and services of special appeal to the singles market, and, of course, there will be parties."

A highlight will be the creation of a National Association of Single Persons, with local chapters in major "singles cities" such as Washington, New York, Chicago and San Francisco. "We may even try to lobby for a White House Conference on Singles."

Hendrickson currently is raising funds for the Expo, which she expects to cost participants $100 each. "We're trying everything. We're even playing the lottery." Although so far she has "zero commitments," several major corporations and foundations "are very interested.

"I'm determined to get the money. After my appearance on The Larry King Show in July we received calls and letters from all over the country from single people who not only endorse the conference, but shared with me their own feelings about being single.

"This conference will be held. I'm convinced that bringing people together to discuss the issue of being single is a major beginning to alleviating both the individual's feelings of isolation and negative societal attitudes about singles. We're not swingers or losers or lonely hearts. We're people who aren't married, and we need to come together."

For more information send a self-addressed, stamped envelope to Singles Expo, c/o The Georgetown Connection, 1656 33rd St. NW, Wash., D.C. 20007.

Conversations, "a new organization for unmarried people with professional and business interests," will launch a series of Sunday-dinner seminars next month, focusing on financial planning. Founder Joan Farrell, owner of Appalachiana in Bethesda, started Conversations "because I'm a single person living in an economically chaotic time and I know there are a lot of others like me."

Each seminar will begin at 4:30 p.m., followed by cocktails and dinner, for $35 (cash bar). Upcoming topics: "Reducing Tax Liabilities on Single Incomes," Sunday at The Seaport Inn, Alexandria; "Financial Planning for the '80s," Oct. 10, Linden Hill Hotel, Bethesda; "Market Timing: The Key to Successful Investing," Oct. 24 The Seaport Inn. Advance reservations are required. Call 657-3357.