It will be the most observed celestial display in history, and tour operators, cruise lines and at least one major museum are offering front-row seats for the unearthly performance: the 1986 return of Halley's Comet.

The packages range from Sun Line's South American cruises, to Mountain Travel's Peruvian trip, to the American Museum of Natural History's Discovery Tour in the Orient. Most have lined up authorities on astronomy as lecturers and hosts, and nearly all will travel to the Southern Hemisphere, where the fiery journey across the sky is expected to be at its most spectacular.

The comet, a ball of dirty ice and gases from the outer reaches of our solar system, has kept a rendezvous with the Earth approximately every 76 years for more than 2,000 years. It flies on an extremely elongated gravity-controlled orbit, will travel around the sun for eight months and then head back where it came from.

Illuminated by the sun, the comet should be visible in the late evening through binoculars, beginning in late November of this year, low in the southwest sky almost anywhere in the Northern Hemisphere. In December, you should be able to make sightings nightly with the naked eye in the same section of the sky. However, in the first few months of 1986, the comet will be brighter when viewed from the Southern Hemisphere. (Viewers in urban areas may be disappointed due to light pollution -- but if the Milky Way is visible, it will be dark enough for you to see the comet. In the Washington area, mid-March is expected to be the best period, with the comet visible in the southeast sky before dawn.)

Serious comet watchers who seek the best possible glimpse of its coma (halo) and 50-million-mile-long tail will travel far from the United States and keep their fingers crossed. Because, of course, there is a certain risk involved, given the vagaries of the weather. (In fact, the Smithsonian Associates travel program will not include a Halley's expedition next year, partly because participants might wind up missing the vital moment.) So the organizations that are sponsoring comet-watching packages are including other activities and attractions as well; for most, the comet is really the icing on the cake. Few are aimed at the low-budget traveler, but many of the trips already are being booked.

The following are among the tours now scheduled; most dates are in 1986 and all prices are per person, double occupancy.

* "Amazon River, Yucatan & Halley's Comet"; "Halley's Comet in Rio"; "Gems of the Caribbean, Orinoco River & Halley's Comet," and "Transatlantic & Halley's Comet." These are cruises aboard the Sun Line's Stella Solaris and Stella Oceanis with departures from Fort Lauderdale, Manaus, Brazil, and San Juan, beginning next January. Rates depend upon the itinerary, which varies in length from 11 to 28 days. Portions of some cruises may be combined.

Among authorities giving lectures on the two ships are Dr. Anthony Aveni, professor of astronomy and anthropology at Colgate University; Dr. R. Lynn Bondurant Jr., chief of the Education Services Division of the National Aeronautics and Space Administration's Lewis Research Center; Dr. Don Campbell, director of the National Astronomy and Ionosphere Center's Arecibo Observatory in Puerto Rico; and Dr. Fred L. Whipple, professor of astronomy at Harvard University and director emeritus of the Smithsonian Astrophysical Observatory.

On the 15-day Amazon journey, embarking Jan. 5 from Manaus, the Stella Solaris will spend six days on the great river, criss-crossing the Equator several times and visiting Santare'm in Brazil. Later the vessel stops at Trinidad, Grenada, Barbados, Guadeloupe, San Juan and St. Thomas. Various scientific and photographic experts will be aboard. Rates range from $2,850 to $5,780 and include one-way air fare from Miami to Manaus (the voyage ends at Fort Lauderdale).

Information: Sun Line Cruises, One Rockefeller Plaza, New York, N.Y. 10020, (800) 468-6400.

* "Peru: Heaven and Earth." Sponsored by the Chicago Academy of Sciences and Chicago's Adler Planetarium, the 16-day adventure will begin March 14 with a flight from Miami to Lima for members of the academy and planetarium (membership in either organization costs $20 for individuals, $30 for a family, and is open to the public).

After two days of cultural and archeological orientation in Lima, Phyllis Pitluga, Adler's senior astronomer, will lead the group on a two-day visit to Nazca in the desert south of the capital. Pitluga, who has been doing research on the mysterious Nazca Lines, will be joined there by Dr. Maria Reiche, who has spent 40 years in Peru mapping the lines and is considered the world's expert on that subject. The Nazca Lines are massive line drawings, including animal figures, that apparently were carved into the desert floor thousands of years ago and may have astronomical significance.

After two days in the desert, the group will visit Arequipa for 2 1/2 days, including an all-night "sky party" to photograph the comet and stars. Other scheduled stops include Cuzco, Machu Picchu and Iquitos on the Amazon, where Dr. Paul Heltne, Academy of Sciences director and a researcher on the river, will discuss ecology and natural history.

Cost: an estimated $2,300, including round-trip air fare from Miami, all other air and land transportation, all accommodations and some meals.

Information: Eliza Houston Davey, membership coordinator, The Adler Planetarium, 1300 S. Lake Shore Dr., Chicago Ill. 60605, (312) 322-0332.

* "In Pursuit of Halley's Comet." The World of Oz lists five expeditions -- to South America; South Africa; Brazil and South Africa; New Zealand and Australia; and Chile.

The 22-day New Zealand/Australia tour, departing Los Angeles March 30 or April 1, includes three nights in Auckland with comet viewings and meetings with the Royal New Zealand Astronomical Society; two nights in Rotorua; three nights in Queenstown -- when the comet will be circumpolar and viewable from sunset to sunrise -- Milford Sound and Mount Cook; two nights in Christchurch; three nights in Melbourne; and stops in the Australian Outback, on the Great Barrier Reef and in Sydney.

Included in the package, priced at about $4,000, are round-trip air fare, hotels, most meals, sightseeing and lectures about the comet.

Information: The World of Oz, 3 East 54th St., New York, N.Y. 10022, (212) 751-3250.

* "Halley's Comet Tour." Mountain Travel, a major operator of expeditions, has packaged a 10-day trip (April 2-11) designed to permit observations of the comet in the predawn skies over Peru.

The group will meet in Lima, where members will visit the planetarium for a lecture. Other stops include a trip to the seaside wildlife colonies at Paracas Wildlife Park and a flight by small plane over the Nazca Lines. Four days of comet watching will be spent in Arequipa, which offers an 8,000-foot elevation and usually clear skies.

Resident scientist will be astrophysicist Dr. David Dearborn. A five-day trek on the Inca Trail to Machu Picchu or a Machu Picchu/Amazon sightseeing excursion are among optional post-trip activities.

Cost is $1,390 and includes accommodations, transfers, charter flight in Nazca, most meals, guides and some sightseeing, but excludes round-trip air fare to Lima.

Information: Mountain Travel, 1398 Solano Ave., Albany, Calif. 94706, (800) 227-2384.

* "Halley's From Peru." PERU tours has scheduled six departures from the United States and Canada to Lima between March 14 and April 11. The tour groups, each limited to a maximum of 30 participants, will spend one day in the capital on arrival and again on departure; three nights in Arequipa, and three nights in Cuzco and Machu Picchu.

C. Luis Vasquez, a Peruvian who is president of the agency, says scientific information on the comet has been provided by astronomer Phyllis Pitluga and dates have been selected to avoid brightness from the full moon that can interfere with observations. Optional visits to the Amazon jungle also are available.

Cost of the comet land package is $355, including airport transfers, accommodations, bilingual guides and some meals. Round-trip air fare to Lima ranges from $484 to $880 -- depending on the airline and departure city.

Information: PERUtours, 38760 Northwoods Dr., Wadsworth, Ill. 60083, (800) For-Peru.

* "Halley's Comet Cruises." The Royal Viking Line has scheduled eight cruises that feature observations of the comet and related lectures. At least one noted astronomer will join each sailing, three of which will be 15-day cruises by the Royal Viking Sky in February and March, between California and Fort Lauderdale via the Panama Canal.

Dr. Carl Sagan, author and professor of astronomy and space sciences at Cornell University, will be aboard two of the other five cruises: on the Royal Viking Sea's 21-day Panama/Pacific trip departing San Francisco (Dec. 19) and Los Angeles (Dec. 20) and visiting Mexican ports (fares from $3,864 to $15,351, including round-trip air fare from 50 North American cities); and on the Royal Viking Star's 14-day South Seas cruise departing Auckland, New Zealand, March 26 with ports of call that include Pago Pago and Suva before arrival at Sydney, Australia (fares from $5,656 to $20,440 -- air fare is extra). The latter is already sold out, but there could be cancellations.

Information: Royal Viking Line, One Embarcadero Center, San Francisco, Calif. 94111, (800) 222-3891.

* "Comet Halley Chase 1986." Combining nightly observations with daytime touring, Astronomy Tours International will send a 15-day expedition to Australia on April 5, and a 16-day expedition to South Africa on April 7.

In Australia the comet watchers will visit Sydney and choose among three options: a trip to Alice Springs and Ayers Rock, with 60 hours of prime viewing in the Outback; about 40 hours of viewing during visits to major observatories; or exploring Canberra and Melbourne (with a total of six hours of observation). There also will be meetings with Australian astronomers, and optional trips to New Zealand or Fiji, or the Great Barrier Reef. Estimated price: $3,500, including air fare from the West Coast, transfers, admission fees, accommodations and most meals.

Leading the Australia trip will be Charles Morris, associate editor of International Comet Quarterly, coleader of International Halley Watch Real Time Monitor Network and author of numerous scientific papers on comets; and Daniel W.E. Green, Smithsonian Institution Astrophysical Observatory astronomer, instructor in astronomy at Harvard University, assistant director of the International Astronomical Union and editor of the International Comet Quarterly.

In South Africa, participants will see Johannesburg; the Sabi Sabi private game reserve on the borders of Kruger National Park, where they will set up their equipment for five nights of viewing and photography; Kimberley and Capetown. There will be meetings with local astronomers and an optional trip to Victoria Falls.

Estimated cost: $3,900, including air fare from the West Coast, transfers, admission fees, accommodations and most meals.

Guiding that group will be John E. Bortle, author of the monthly column, "Comet Digest," in Sky and Telescope magazine; and Anthony Cook, advanced amateur astronomer and Halley's Comet lecturer at the Griffith Observatory in Los Angeles.

Information: Astronomy Tours International, 19143 Victory Blvd., Suite 13, Reseda, Calif. 91335, (818) '% 5-0448.

* Halley's Comet Theme Cruise." Passengers will be peering through their binoculars -- telescopes tend to be a bit shaky afloat -- when the Cunard/NAC's Vistafjord makes a 14-day cruise to Rio de Janeiro on May 15, and then begins the return cruise from Rio on May 29. Apollo astronaut James Irwin and Dr. Francis Drake, an official of the Planetary Society and dean of the Division of Natural Sciences at the University of California at Santa Cruz, will give lectures.

The vessel departs from Fort Lauderdale, stopping at Caribbean and Brazilian ports. Rates for each segment, including the flight to or from Rio, range from $2,990 to $6,370. There is an optional tour of Brazilia.

Information: Cunard/NAC, 555 Fifth Ave., New York, N.Y. 10017, (800) 221-4770.

* "Oriental Passage: Singapore to Athens." This tour is designed and operated by the American Museum of Natural History's Discovery Tours.

Halley's comet "is an evening activity," notes Todd Nielsen, manager of the travel department, and those several hours devoted to viewing the skies do not constitute sufficient material around which to build a voyage. So the museum's promotional literature treats the comet in low-key fashion. It emphasizes instead the "outstanding cruise" aboard the small (74 cabins), highly rated Illiria along the ancient maritime silk route at a time expected to be the highpoint of Halley's performance.

The cruise embarks from Singapore April 6 and will be sailing through the Strait of Malacca when viewing should be at its best. Eight lecturers will be aboard, including Dr. Thomas D. Nicholson, director of the American Museum of Natural History and former chairman of the museum's Hayden Planetarium, and experts in such fields as marine biology, geology, anthropology and art history.

While the comet will be carefully observed, the journey is designed primarily with broad cultural aspects of the region in mind and it covers an area stretching from Singapore to Thailand, Burma, India, Sri Lanka, the Arabian Sea, the Red Sea, Egypt, Jordan and Greece. Rates range from $8,995 to $10,245, exclusive of air fare but including all lectures and land excursions.