THE UNITED States soon may become the only industrialized nation in the world without railroad passenger services connecting its major cities.

By this time next year, for example, you may not be able to travel on the National Limited from Union Station to Kansas City. The Floridian between Chicago and Miami may be canceled. Southern Railway may halt the only train service from Washington to Atlanta and New Orleans. Long train trips from Chicago to the Pacific Northwest may be remembered only in history books.

Such drastic cutbacks appear inevitable unless the Carter administration and Congress are prepared to change their policies on spending for Amtrak, the subsidized national rail passenger corporation, as spelled out in recent actions.

Stated briefly, the administration's policy to date has been to hold the line on Amtrak's subsidies at current levels of about $500 million a year. Since costs continue to rise, however, the only way for Amtrak to balance its annual budgets under such a policy is to reduce services each year in an amount equal to inflation in expenses.

Orren Beaty, president of the National Association of Rail Passengers, told Secretary of Transportation Brock Adams recently that such a ceiling on aid means rial passenger service will be well on its way to extinction. With forced cutbacks in service every year, Beaty added, "nothing will be left but a few corridor services," such as between New York and Washington.

No American is more perplexed about the current situation than former rail industry executive and current Amtrak president Paul Reistrup. He said in a recent interview with The Washington Post, "We can't keep chopping service, especially since we really have got the thing (Amtrak) going."

Reistrup also urged Congress to make the kind of decision America's government does not often embrace: Either make a commitment to inter city passenger service by assuming there will be continuing subsidies and benefits to the public, or do away with Amtrak altogether.

Since Amtrak was founded by Congress in 1971, the pressure from Capitol Hill always has been for more and more service. But intercity passenger service is a money-losing business on virtually any route in the world today, because if fares were priced at a level to match costs, there would be no riders. Thus, more service always costs more money.

If the United States wants intercity trains, said Reistrup, "then its funding level should permit such a system to be developed and operated properly." If not, "maybe we should eliminate it entirely," he added.

To the average traveler or taxpayer seeking clues for an understanding of the future for rail passenger service, the conflicting reports, pronouncements and government decisions in the past four months would appear to be a monumental case of a schizophrenia.

One day, the news media reported that notices soon would be posted around the country detailing cutbacks in trains and service scheduled in the next month or so. A month later, the public was treated to Amtrak's five-year plan, a blue-sky scenario of new passenger cars, engines and expanded services that had nothing to do with reality but which presumably pleased rail passengers.

Then, in true perils-of-Pauline style, Amtrak threatened cutbacks without more federal aid, got little response and actually started the cut-backs, got some money and reinstated some service, initiated other cutbacks because the extra money wasn't enough and, finally, suspended the latest cutbacks when Congress coughed up a bit more dough. For a week, the Floridian was being dropped from Amtrak's schedules in January; now, that cancellation has been withdrawn.

All the while, some intercity rail service has deteriorated - notably aboard the East Coast Metroliners. But the federal government is pouring millions of dollars into improvements along the Boston-Washington routes, new contracts with operating railroads and recently completed track work have permitted better service. In September, nearly 69 per cent of Amtrak trains were on time compared with about 60 per cent in August (but Metroliner were on time only 26 per cent of all trips, down from 30 per cent).

So there is a mixture of good and bad reports about the current level of Amtrak service, which does not permit an easy assessment.

In terms of the total U.S. govenment budget for the current fiscal year 1978, which projects spending of $458.25 billion and a deficit of $61.25 billion, Amtrak's subsidy is not a major factor.

Originally, the passenger corporation asked for $534.1 million to underwrite losses from rail service this fiscal year. The administration, supposedly one that favored rail passenger transportation, asked for $500 million. Congress came up with $488.5 million for the year that began Oct. 1. And Amtrak, faced with a defict of more than $50 million, began taking steps to cut service.

At first, Senate and House appropriations conferees approved an additional $8 million. But when Amtrak directors responded by voting to cancel the only Chicago-Florida service and to speed up the process by which other trains would be dropped in a few months, Congress added another $10 million. The conference committee also bought some time by ordering Amtrak to stop making plans to cancel any existing services until a new Department of Transportation reexamination of Amtrak routes is prepared by March.

But the problem of financing Amtrak - or if America even wants an Amtrak - remains. Athough public opinion polls show Americans in support of passenger trains, few people ever ride what remains of a vast system that connected most communities by rail several decades ago.

Even Southern Railway, a Washington firm that elected to keep its paasenger system outside Amtrak and to add up losses as a worthwhile public relations expense, is thingking of dropping its remaining Crescent from Union Station to Atlanta and (threee times weekly) on to New Orleans.

In the fiscal year ended last Sept. 30, Amtrak carried 19.2 million riders compared with 18.15 million the previous year and 17 million for its first full year of operations.

Measured against earlier years, however, the recent increase in ridership shows that rail travel is not popular. Back in 1944, railroads reported 90.23 million passenger miles traveled. With the availability of money, and gasoline after World War II, Americans' love affair with the automibile was confirmed and rail travel was down to 39.9 million passenger miles by 1947 and to 14 million by 1964. The total hit a low of 4.3 million in 1972 before starting slow climb to about 6 million today, more than 4 million of which is attributable to Amtrak.

All the while, Americans are buying cars in record numbers. General Motors Corp. chairman Thomas A. Murphy siad his firm and the auto industry faces sales records in 1978, including 11.75 million new cars. People buy cars "not because they want to be ostentatious, or anything like that, they buy them because they nedd that type of vehicle to handle their transportation needs," Murphy said. "I deeply resent as an American (the idea) that we are going to interfere with people's freedom, we don't want them to have the capability to carry the family in one automobile," the GM chief executive added.

For Amtrak, looking at its less than 1 per cent share of current intercity travel vs. 87 per cent for the auto, 11 per cent for air and 1.5 per cent for bus, the current controversy over its financing adds up to a critical cross-roads. Either Amtrak will be permitted to develop a gradual increase in market share or it will see its potential growth destroyed by cutbacks in service (even a reduction to three times weekly from daily service in certain trains means fewer riders overall, Reistrup pointed out).

To be sure, Amtrak has a goal of major improvements and development of new high-speed trains outside the Northeast Corridor - such as Chicago-Detroit and Los Angeles-San Diego. Increased frequency would be added between Los Angeles and San Francisco and Chicago and Pittsburgh. New trains would be added in such markets as Cincinnati-Dayton-Columbus. A total of 353 new passenger cars would be purchased.

Amtrak projects that its ridership under aggressive marketing could be boosted 29 per cent in the next five years to 26 million by 1982. Revenues would grow from $287 million to $482 million. The cost of this plan: an operating subsidy over the five years of $3.5 billion, or $695 million a year, plus grants to buy equipment of $1.05 billion or $210 million a year.

If just 1 per cent of auto travelers shifted to trains, says Amtrak, revenues would jump from $371 million to $527 million in 1980. This change would save 600,000 barrels of oil annually.

But instead of planning this future growth, DOT officials, members of Congress and Amtrak officers in 1978 appear destined to be studying potential cutbacks to reduce subsidies, mainly by restructuring Amtrak's system of routes. In the process, service to some communities will be eliminated.

Barring a policy shift that would earmark a larger share of the federal budget for Amtrak, it appears certain that the Floridian between Chicago and Florida will be stopped. Last year, that train operated with a loss of $10 million.

Other potential targets for cutbacks include the National Limited, with separate sections from New York and Washington to Kansas City; the Empire Builder, between Chicago and Seattle via Minot, N.D.; the North Coast Hiawatha, between Chicago and Seattle via Billings, Mont.; the Inter-American, between Chicago and Laredo; the Lone Star between Chicago and Houston; and the San Joaquin, between Oakland and Bakersfield.

"It seems irrefutable that Amtrak's forward momentum has been halted, and there is a danger that a 'negative snowball' has been set in motion," said a recent editorial in the National Association of Railroad Passengers newsletter.

The current debate has focused on costs, the association argued, but revenues could be boosted by increased service frequency (not less) and costs per mile of service could be reduce. "Stated bluntly, it is irresponsible to fund the basis foundation for a nationwide system, and incur all those fixed costs (about $3 billion has been invested or committed), and then refuse to pay for operation of a meaningful level of service."

NARP has many friends for passenger service on Capitol Hill and there will be congressional elections next fall, so a short-term increase in aid for Amtrak is possible next year to prevent immediate curtailments.

But, as in the Ford administration, there is little support today in the Office of Management and Budget for increasing Amtrak's allocation of money under a President committed to balancing the budget. And Amtrak gets no visible support for increased funding or promotion of rail travel inside the rail industry itself, although the public thinks of railroading in terms of passenger service rather than its predominant role as a carrier of freight.

Unless the government is prepared or pressured to make a longer-term commitment to rail passenger service, a new era of decline appears on the horizon less than a decade after the Amtrak experiment was started.