QUESTION: We plan to visit England soon. I remember reading about a disease affecting cows in Britain. Is beef consumption considered safe now?

ANSWER: There have been no reports of humans being infected with bovine spongiform encephalopathy, a disease that causes fatal brain disorders in cows. However, judgments vary about whether it is safe to eat beef in Britain.The disease, also called mad cow disease because cows stagger, fall and sometimes behave violently when the disease affects their brains, was first diagnosed in cows in 1986.

It was last year, however, after the death of a pet cat suffering symptoms of the virus, that the public began expressing a fear that humans might get the disease; it was never known whether the cat ate beef.

There was a drop in beef purchases in Britain, and some European countries temporarily banned British beef.

It is still not known how the disease is spread among cattle.

One theory is that it is passed along genetically, and another is that it is caught when cattle eat feed made from sheep infected with a similar disease. (Spongiform encephalopathy develops in older animals; as sheep are generally slaughtered when they are young, lamb is not considered as dangerous as beef.) Since 1988, authorities have been destroying all diseased cattle.

A government investigation last year concluded that there is no risk to human health from beef. The government said its panel of scientists found that the disease can be passed along only through the animal's nervous-system tissue and that current regulations insure that brain and other nervous tissue are removed.

Richard Lacey, a professor of medical microbiology at Leeds University, said that during slaughter, brain tissue may get onto meat. Scientists expect the virus to have an incubation period of perhaps 20 years in humans, he said, so it will be some time until it is known if the disease can be passed to people.

He said he would advise people against eating beef until there is more information about the way in which the disease is transmitted and added that there is no test to determine if the virus is present in humans.

Dr. Tim Lang, spokesman for a British consumer watchdog group, Parents for Safe Food, said that "a huge amount of research is being done" and that new discoveries are constantly being reported. He said that he did not believe there was enough information yet, but that, although he preferred not to eat beef, he thought the risks were minimal.

QUESTION: I am interested in the Orient Express, getting on in Venice and leaving the train in Istanbul.

ANSWER: You can take a conveyance called the Orient Express from Venice to Istanbul, but it is a cruise ship that connects with one of two trains that now bear the Orient Express name. (The original Orient Express train began running in 1883, traveling between Paris and what is now Istanbul, and it stopped service in 1977.)

The ship connects with one of the trains, the Venice Simplon-Orient-Express. That train has two main routes: One goes between London and Venice, a trip of 32 hours, with stops in Paris, Zurich and Innsbruck; the train started service on this route late last month and it will continue until mid-November.

The other route is between London and Budapest, 34 hours, the train stopping in Paris, Zurich, Innsbruck, Salzburg and Vienna; service is from early June to early November. The cost from London to Venice or Vienna is $1,440 a person one way or $2,090 round trip, based on two in a cabin.

The cost of the cruise, which also makes stops in Greece, is $1,465 to $2,315 a person, depending on accommodations, based on two in a cabin. Passengers can leave the ship at any stop and re-embark for a later sailing. Reservations: Venice Simplon-Orient-Express, 1155 Avenue of the Americas, New York, N.Y. 10036; (800) 524-2420.

The other train is the Nostalgic Istanbul Orient Express. One itinerary, departing Sept. 7 this year, leaves Istanbul, and stops at Edirne, Turkey; Sofia, Budapest, Vienna, Salzburg and Munich and arrives in Zurich Sept. 10. The cost is $3,960 a person with two in a cabin. There are also routes between Zurich and Nice, May 11 to 13, and Prague and Dresden, in late November and early December. Reservations: 104 South Michigan Avenue, Chicago, Ill. 60603; (800) 289-7245.

QUESTION: In November, my family and I were bumped in both directions between New York and Florida. For compensation we were given coupons for travel anywhere that Eastern flies. With Eastern out of business, isn't it anyone's responsibility to pick these up?

ANSWER: It is not the responsibility of any other airline to honor vouchers from Eastern.

Continental Airlines, part of the company that owned Eastern, is among the airlines accepting Eastern tickets but it will not accept free-travel vouchers.

In a survey of several other airlines, none said they would accept the vouchers. A spokesman for Continental said that Eastern ticketholders will be entitled to refunds resulting from bankruptcy proceedings, and so will airlines that accept Eastern tickets. But, he said, vouchers have no such value, and for that reason airlines will not be inclined to honor them.

Passengers who are involuntarily bumped from an overbooked flight are entitled to substitute transportation and, if they arrive at their destination more than an hour later than originally planned, $200 to $400 in addition, according to Department of Transportation rules.

Airlines may offer free transportation on future flights in place of a check, the department says, but passengers have the right to insist on a check. Passengers who volunteer to stay off an overcrowded flight in return for a voucher are not entitled to anything additional.

In both cases, once passengers accept the vouchers, the airline has no further legal obligation. QUESTION: I will be driving to Mexico City in May. I have heard that there are limitations on days when one can drive there .

ANSWER: To cut down on pollution, Mexico City prohibits the use of cars registered in the city on one weekday, the day determined by the last number on the license plate: Monday, 5 or 6; Tuesday, 7 or 8; Wednesday, 3 or 4; Thursday, 1 or 2; Friday, 9 or 0.

While foreign tourists are not mentioned in the regulations, city officials say the restrictions apply. Many Americans have been stopped and fined (about $100) or had their cars towed on days their license number indicated.

NYT-03-25-91 1303EST