The O'Dochartaighs are planning a family reunion in the Republic of Ireland and Northern Ireland this summer. And they expect it to be one of the biggest clan gatherings ever held in the "old sod," with official ceremonies, pageants, music, dancing, private family visits and sightseeing in history-filled cities and the surrounding countryside.

There are hundreds of thousands of Dochartachs (and their relatives) around the world, so the sponsors of the celebration hope that upwards of 5,000 will attend between June 16 and July 10. A majority of the visitors will come from the United States, where the largest group of Daughertys -- perhaps 200,000 strong -- now resides. About 17,000 of the clan remain in Ireland, and 7,300 live in Scotland.

Sure 'n' for the Daughartys, O'Dougherties, Dockertys and Doritys -- there are about 110 different spellings of the name, which means "people of the oak houses" -- it will be almost like having two St. Patrick's Day celebrations in the same year.

Tourist boards of both Irelands are helping out with the planning; tour packages range from independent travel with only air transportation and reunion registration included, to a fully escorted 10-day tour.

The 1985 O'Dochartaigh International Reunion is the brainchild of Jack Dougherty, a business executive in New Castle, Del., and reunion director; Patrick Dougherty, president of the O'Dochartaigh Family Research Association in Attica, Mich., and Patrick L. Doherty, director of Inter-City Development in Londonderry. Planning for the project began five years ago. Reunion director Dougherty says that he's optimistic about the turnout, noting that a few hundred Irish in Australia and New Zealand have already chartered a 747 for the trip and an inquiry was even received from China:

"I'm sure, as our forebears took their last look at those green shores, they left a big part of the soul in Ireland. Now is our time to return to Donegal and claim our roots and our heritage . . ."

Londonderry city officials have purchased a bank of computers and are setting up a genealogical research facility to assist clan members who want to look up their family trees. There will be no charge to reunion registrants. (Although success in tracing ancestors often depends on preliminary research and how much detailed information is fed into the computers.)

McShea Travel of Gaithersburg and Rockville, Md., is the official tour packager-operator and the exclusive retailer for the reunion in the United States. The agency offers four tours (all include round-trip air transportation from New York or Boston to Dublin, pre-planned reunion activities and registration): Tour A, with no additional features, costs $599 to $649 per person; tour B, which also provides a compact rental car with unlimited mileage, costs $749 to $799 per person; tour C includes all features of A and B, plus sightseeing tours of Dublin and Irish Folk Park, admission to Blarney Castle, six nights of bed-and-breakfast accommodations around both Irelands and all service charges and taxes, for $799 to $849 per person, double.

Tour D, designed by the Family Reunion Association, is the guided package with first-class hotels in the Irish Republic for eight nights, full Irish breakfast daily and sightseeing during an itinerary that begins with arrival at Dublin Airport on June 22 after an overnight flight.

It takes the traveler across the border of Northern Ireland, first to Enniskillen and later to Londonderry, second largest city in that troubled country, where ceremonies honoring the clan will be held. It then travels around the Republic from Donegal to Galway to Killarney and, finally, to Shannon Airport on June 30. Cost: $1,049 per person, double, including airport transfers, porters, service charges and taxes.

More information from McShea Travel, 6240 Montrose Rd., Rockville, Md. 20852, (800) 638-6681.

* VENEZUELA ADVISORY: If you're planning to be in Venezuela between Jan. 26 and 29, when Pope John Paul II has scheduled his visit, the State Department advises that hotel accommodations will be difficult to get on the indicated dates in these cities: Caracas, Jan. 26-27; Maracaibo, Jan. 27-28; Me'rida, Jan. 28; Puerto Ordaz, Jan. 29.

Venezuela's domestic airlines will be overbooked to and from those cities, the State Department says, and roads will be crowded. It warns Americans they should have confirmed reservations in hand before entering the country and to expect that public services will suffer from "a high rate of absenteeism."

* HALLMARK GREETING: Hallmark Cards Inc. marked the 75th anniversary of its founding by opening a $1.5-million, 10,000-square-foot Visitors Center last Thursday at the company's international headquarters in Kansas City. It is designed to greet 100,000 to 150,000 guests annually.

Presenting an overview of the company and the industry, the center features displays of cards from the firm's history that include examples of humor from the Depression era, World War II sentiments for servicemen and holograms from the '80s. There are also films and exhibits showing how Hallmark products are produced: A master engraver creates metal dies; pressmen run cards through a press that applies foil; a bow-making machine operates at the push of a button.

The center is open from 9 a.m. to 5 p.m. weekdays and 9:30 a.m. to 4:30 p.m. Saturdays. Admission is free.

* UNDERWATER PARK: One of the Caribbean's newest tourist attractions, "Curac,ao Underwater Park," has just completed its first year of operation. Extending for about 12 miles along the Dutch island's south coast, it has been popular both with scuba divers and other visitors, who can view coral-reef life by snorkeling or from glass-bottom boats.

Curac,ao, largest of the Netherlands Antilles, lies 35 miles off the coast of Venezuela. The 1,500-acre park, funded in part by the World Wildlife Fund, was planned to protect the reef's ecology while making it more available to the public.

The park begins just beyond the Princess Beach Hotel on the outskirts of the capital, Willemstad, with an underwater nature trail that uses concrete markers on the shallow ocean floor to guide snorkelers and identify the different types of coral, plant life and fish. The trail runs 975 feet to the wreck of the HMS Orange Nassau, which sank in 1906: The wheelhouse roof rests just below the surface, providing a rare opportunity to explore a sunken ship without the need to dive.

Each Saturday from Feb. 2 until May 25, the Travel Committee, a local tour operator, will offer one-week charter packages to the island, including hotel accommodations and round-trip non-stop flights on ALM Airlines from Baltimore International Airport. Prices start at $369 (plus 15 percent for service charges and tax) and vary according to travel dates and hotel selection.

For more information: Curac,ao, P.O. Box 1446, Radio City Station, N.Y. 10101-1446; the Curac,ao Tourist Board, 400 Madison Ave., Suite 311, New York, N.Y. 10017, (212) 751-8266; the Travel Committee, 110 Painters Mill Rd., Owings Mills, Md. 21117, (301) 363-4900, or a travel agent.