Concerns raised recently by the U.S. government about the safety of American travelers in India and Mexico have been eased.

India is recovering from the rioting that followed the assassination of Prime Minister Indira Gandhi on Oct. 31. U.S. tour operators report that some group departures to India were canceled because of the turmoil, but others left as scheduled after clients were given the option of dropping out and receiving a full refund. Immediately following the state funeral last month, many tourists who did decide to abort their trips sought new bookings on departures set for early next year, said one major operator. Another firm, however, has been experiencing reduced demand for its 1985 India packages.

The Mexican government, with a less serious problem, has stepped up efforts to police its highways and increase visitor security. This program was outlined last month, following word in October that the U.S. Embassy in Mexico City intended to ask the State Department to warn Americans about the danger of being attacked while driving on certain roads. (As a result of Mexico's action, the embassy shelved the request for a travel advisory.) There was no subsequent drop in U.S. tourism to Mexico, where the important winter high season has just begun.

Canceling travel advisories on India issued earlier, the State Department said it no longer advises against travel to New Delhi and Northern India and noted that the atmosphere in the capital is "much improved." A curfew has been in effect in most parts of New Delhi from 11 p.m. to 4 a.m. Buses and taxis have been available.

"Americans should continue to exercise caution, avoid crowds and observe the curfew where imposed," the State Department said. It added that long-distance telephone calls have been difficult to make, and scheduled transportation between cities outside the capital is subject to delays.

Visitors who arrive in New Delhi by air during the curfew should contact the police poast at Palam Airport for a pass. If a pass cannot be obtained, a passport and airline ticket probably will permit passage to and from the airport, according to the State Department.

U.S. citizens should register upon arrival with the American Embassy in New Delhi or with the American Consulate in Bombay, Calcutta or Madras, the State Department says. For up-to-date information on current conditions, call the department's Citizens Emergency Center at 632-5225.

Kanta Thakur, regional director of the India Government Travel Office in New York, is optimistic about the future: "Travel from the U.S. to India had been increasing each year, especially in the last three years, with a 20 percent rise during the first five months of 1984. We still feel that India has been established in this country as one of the major popular travel destinations." She sees the current period as a "purely temporary setback," and feels that group business will pick up during the next two months.

Mexico's Ministry of Tourism announced that a 24-hour emergency telephone hotline would go into service early this month for travelers needing guidance. This supplements the teams of "Green Angels" who continue to patrol the country's highways. They provide free, basic automobile repairs for stranded tourists, communications assistance and emergency medical aid.The hotline number if 5-250-01-23.

Jorge Gleesen, head of the green-uniformed "Angels," was quickly sent on a good-will tour of the West and Southwest, the two U.S. areas from which most motorists enter Mexico. The Green Angeles now include more than 1,000 staff members and operate 260 vehicles, most of them radio-equipped and linked with 42 fixed bases throughout Mexico.

The Mexican government, noting the U.S. Embassy's reference to a rash of violent assaults on visitors (including two murders), said that 17 million Americans have traveled safely in Mexico during the past five years.Mexican officials said that the list of 51 incidents cited included "automobile and sports-related accidents" in addition to instances of robbery and criminal violence, but promised increased efforts to insure the safety of visitors.

The American Automobile Association has warned its members that there is danger on Mexican highways. It urges motorists to be careful, advising them against driving at night and sleeping in their autos. The AAA also points out another problem: Unleaded gas is difficult to obtain outside major Mexican cities, creating the possibility of destroying catalytic converters by using the wrong fuel.

"There has been a tremendous increase in cross-border traffic in the last year and a half due to devaluation of the peso," explains Vince Hodgins, director general of the Tourisn Ministry officein New York. Everyone is looking for no-lead gas, Hodgins says, but many service stations operated by Petroleos Mexicanos, the government-owned oil monopoly, are not equipped to supply it. Pemex recently started a program to upgrade and modernize the stations, which will result in more outlets selling unleaded fuel, he says.

As low prices and a warm sun continue to draw visitors to Mexico, Hodgins has a confident prediction based on advance bookings: "It looks like the best winter season ever."

*"VISIT WITH SANTA: No one is offering tours to Santa's Workshop at the North Pole, but children with visions of sugarplums and toys can take a vicarious trip by mail.

The Finnish Tourist Board says that all letters addressed to "Santa Claus (or Father Christmas), the Arctic Circle, Finland," and received no later than Dec. 23, will be answered. (Postage is 40 cents per half ounce.) Santa is already busy with his elves at his headquarters in Rovaniemi, Finnish Lapland. Last year more than 75,000 letters in many languages were received by St. Nick from around the world; each response carries an authentic Polar Circle stamp.