With fuel costs rising by the week, airlines, trains, bus lines and cruise ships have to increase rates.

You can expect a series of fare hikes this year in every mode of transportation. But there are ways to protect yourself against fare hikes on certain types of trips.

In the past, domestic airlines have adhered to an informal guideline of not adding fare hikes to tickets previously purchased and picked up. If you buy an airline ticket, say, a month before your departure date, and you pick it up and pay for it, you're set -- provided you don't later make changes in your itinerary. If the price is raised in the interim, you don't have to pay more. Tickets for reservations that have not been paid for are vulnerable to price hikes when the passenger picks them up before flight time.

Two airlines, Western and Texas International, have asked the Civil Aeronautics Board to drop the informal rule on guaranteeing air fares to passengers who pay ahead of time.

The airlines say fuel costs are rising so fast, they can't keep up. This is prompting price hikes every two or three months.

The CAB doesn't want to give up the guaranteed-fare concept. On the contrary, a proposed rule would make it mandatory for airlines to guarantee fares to passengers who have paid for their tickets in advance. Foreign travel has its own rules. If you're flying abroad with a foreign airline, you may have to ante up for a fare increase at the gate even though your tickets have been paid for. With American-owned airlines flying overseas, your fare is generally protected if you pay in advance.

When you make your air travel plans, it's a good idea to ask the ticket agent or travel agent about the airline's guaranteed-fare policy. If you pay in advance and have your tickets in hand, will you be subject to any fare increase?

With train tickets, AMTRAK says that fare increases are normally announced 30 days ahead of time. If you buy your ticket before the announcement, you're protected against the fare hike. If you buy after the fare hike is announced, for travel after the effective date, you have to pay the increased fare.

With most bus lines, you get no protection at all. if you buy your ticket ahead of time, you might have to pay an additional fare when you board the bus. So, there's no point in getting your tickets in advance.

When you book a cruise on an ocean liner or a package tour, you're also subject to possible price increases after you've paid for your tickets. In some cases, you can refuse to pay the price increase and get your money back. In others you cannot. A lot depends on how the cancellation deadline is worded.

If you're planning on a packaged tour or cruise, your best bet is to get all the price information explained by a good travel agent.

Know what you might be up against -- ahead of time. If there might be some increase in the fare, have the agent explain how much it's likely to be.