AUSTRALIAN and New Zealand meteorologists say that the short-term weather patterns for a large part of the globe are changing because of a warm Pacific Ocean current.Australia and the eastern part of New Zealand will experience a drought, the normally arid coastal areas of Ecuador and Peru will be wet, and the southern half of the United States will have a wetter than normal winter. Meteorologists expect the weather shift to last through March or April of 1992. The shifts are caused by a weather phenomenon known as "El Ni (the Child), a name coined at the end of the last century to refer to a warm ocean current that appears off the coast of Peru at around the time of Christmas every three to five years. The El Nino phenomenon is a complex interaction of ocean currents and temperatures in the Pacific. Periodically, these currents and temperatures change in a manner that dramatically affects the weather. Meteorologists now say they believe this is happening. "It appears to be just emerging," says Bill Kininmonth, superintendent of the National Climate Center in Melbourne. "It is expected to intensify over the next couple of months," says Brett Mullan of the New Zealand Meteorological Service in Wellington. Long-range weather forecasters determine that an El Nino is in effect by watching the barometric pressure differences between Tahiti and Darwin (capital of Australia's Northern Territory). When the pressures in Tahiti are lower than the pressures in Darwin, it may indicate that the El Nino effect is taking place. At the same time, the normal easterly trade winds are weakening. Another clue that the weather is changing is the sea temperature. Water temperatures in the eastern part of the Pacific are now rising rapidly as they have during other El Ninos. At the moment, the water is two degrees warmer than usual. During the 1982-83 El Nino - the last major shift - the water temperature in the ocean rose by five degrees. Although some of the meteorologists are convinced the El Nino effect is beginning, others are still cautious. Gerd Dowideit, a lecturer at the University of Queensland, says there is an 85 percent chance of an El Nino. Barry Hunt of Commonwealth Scientific and Industrial Research Organization's Center for Drought Research says he believes it is still too early to make predictions. "We had the wettest June on record in Melbourne despite the fact El Nino is supposed to be on the way," Mr. Hunt says. But there is other anecdotal evidence of an El Nino. During an El Nino, the band of rain over the South Pacific shifts. It has now moved away from Fiji, where some weather stations are reporting a drop of 75 percent in their monthly rainfall. Instead, the Pacific rainfall will move to northerly islands, such as those in the Kiribati group near the equator. In New Zealand, the winds have shifted more to the south, bringing cold weather from Antarctica. "It is the coldest June since 1976," says Mr. Mullan. There are even reports of sheep frozen to the ground. If the El Nino effect is starting, it could disrupt the world's agricultural markets. The anchovies, for example, will move away from the coast of Peru because the normally cold Humboldt current will shift. These fish are an important food source. In the past their disappearance has pushed up the price of soybeans, which are sometimes used as a substitute food source. Unfortunately for Peru and Chile, the warmer water results in rain in normally arid areas. This has already caused flooding in some parts of South America. It could also result in less rainfall on the Asian subcontinent during the monsoon. This could lower the output of rice crops. In South America, the shift in the El Nino has affected the rain in Brazil and Venezuela. Rainfall is much lower in the July-to-October period, when it is normally wet. This could affect crops in these countries. In Australia, the weather shift usually results in a drought in most of the inland areas. During past El Ninos, the sugar cane crop in Queensland has suffered. "It increases irrigation cost and can result in stressed cane and lower sugar content," says Christine Walker of Canegrowers, a trade group, in Brisbane. A bad crop next year is expected to follow a bad crop this year. For other farmers the drought is also coming at a bad time. "Coming at this time it could mean just about the end," says Howard Moxham, an officer of the New South Wales Farmers' Association. Sheep growers in Australia are still struggling with wool prices 40 to 50 percent lower than last year. And, wheat farmers are unhappy with low prices and subsidized competition from the United States. "Farmers are having extremely hard times," says Mr. Moxham. On the positive side, the farmers received excellent rainfall in June after their crops were planted and will enter the drought with a good crop. The El Nino also could have an impact on tourism. In the past during El Ninos, it has been wetter than normal in the southern United States. This could drive tourists away from Walt Disney World in Florida and other southern resorts. But the dry conditions in Australia should make the summer tourist season superb. In New Zealand, however, the west coast will be wetter than normal while Auckland and the east coast sizzle.