Planning a smoke-free vacation takes some doing: Smoking regulations vary from city to city, state to state and nation to nation, and within individual sectors of the travel industry. You might imagine there'd be some kind of one-stop Web site, guidebook or other comprehensive resource to help identify smoke-free havens for travelers in the United States and abroad -- but you'd be wrong. Still, with a little phone work and mouse-wrangling, you can cobble together a butt-free, lung-friendly trip. Here are some tips to get you going, but beware: No-smoking policies are constantly shifting.

* ON THE WEB. A handful of well-meaning Internet sites offer roundups, some more thorough than others, of non-smoking options. Action on Smoking and Health (ASH) charges a one-time $25 fee for access to its smoke-free travel listings on www.ash.org. You'll find a smattering of U.S. and international hotel listings, but little in the promised areas of air travel, tours and cruises, and rental cars. The American Nonsmokers' Rights Foundation (www.no-smoke.org/lists.html) keeps track of no-smoking ordinances in U.S. municipalities and states (as does Ash.org, which also offers this info free of charge). Tobacco.org (www.tobacco.org) reprints news articles regarding tobacco laws, including helpful information about regulations in whatever part of the world you're visiting -- but you'll have to dig to find it.

Most useful of all is Smoke Free World (www.smokefreeworld.com), which lists tons of info in several languages about non-smoking travel, lodging (including home-exchange organizations that offer smoke-free house swaps), dining and entertainment worldwide. It's a bit catch as catch can, but it's full of helpful tidbits, including an international phrasebook listing ways of saying "no smoking" and "smoke-free" in 18 languages. (In Bulgarian, for instance, "ne pushete" means "don't smoke.") Unlike many other smoke-free sites, SFW is refreshingly free of political agenda.

* HOTELS. The Web site for AAA (www.aaa.com) lists nearly 32,000 hotels nationwide, including almost 4,000 properties that are totally smoke-free; the online search is free to all, not just members. (Its hotel guide includes a "No Smoking Rooms Available" search option when you click on "Specify Additional Criteria.") Going to Europe? Try NonSmokingZone.com (www.xbert.com/nonsmokingzone/index.html), which offers a limited list of smoke-free accommodations (and some restaurants) in Great Britain and the Continent. Another option -- http://british-hotels.com/Site/hotels_search_for_no_smoking.asp -- does the same, but just for the United Kingdom.

* RESTAURANTS/BARS. Advance planning requires an up-to-date guidebook, a savvy travel agent or a good Google search. But once you're in town, ask locals, hotel employees or staffers at an area tourism office where the non-smoking joints are.

* AIR TRAVEL. Smoking is prohibited on all domestic and most international flights; check ASH's Web site (http://ash.org/nosmokair.html) for a chart, which was updated last September and lists smoking policies on airlines the world over. (Unlike the service listed above in On the Web, this Web page is free.)

Smoking is restricted at most U.S. airports, too. At Reagan National, it's permitted only on the outside terraces on the upper level of the B and C terminals and in select restaurants; at Dulles, smoking's allowed only in designated lounges on midfield concourses B and C; and at BWI indoor smoking is allowed only in the pub area in O'Brien's restaurant. Go to www.no-smoke.org/smokefreeairports.html for a listing of U.S. airports in which smoking is entirely prohibited, and www.no-smoke.org/smoke_air_25.html for smoking policies at the nation's 25 busiest airports.

* TRAINS. In the United States, smoking is prohibited in all Amtrak stations, on all buses connected to Amtrak service and, for now, on all but four Amtrak trains. Starting Nov. 1, only one, the Auto Train running from Lorton, Va., to Sanford, Fla., will allow smoking but only in designated areas. Details: 800-USA-RAIL, www.amtrak.com.

On Europe's train system (www.eurail.com), smoking policies are set by the country from which the train departs. Eurail spokeswoman Nora Brossard says all trains have nonsmoking carriages and that a majority of the cars throughout the system are smoke-free.

* RENTAL CARS. Major rental agencies offer smoke-free vehicles to those who ask, but procedures for securing such a car vary. At Thrifty (800-THRIFTY, www.thrifty.com), for instance, all the vehicles are supposed to be smoke-free, but the rule is hard to enforce. Sniff around when you get your car, and if it smells smoky, insist on another. Other agencies like Avis and Budget offer smoke-free options by request, and for no additional charge.

* CRUISES. Most cruise lines have designated nonsmoking rooms and other areas. But if you're looking for a total smoke-free cruise, you're out of luck. Carnival's Paradise discontinued its smoke-free policy on Sept. 5 and now allows smoking in designated areas.

-- Jennifer Huget