Although few Americans would choose passenger trains today for trips over 100 miles, a majority favor improvements in the quality and availability of rail travel, pollster Louis Harris reported yesterday.

Detailing results of a nationwide public opinion sampling, conducted by Louis Harris & Associates at the request of Amtrak, the pollster told a National Press Club news conference that a growing percentage of Americans believe they will travel by train more in the future.

The Harris report was based on telephone interviews between Feb. 11 and Feb. 22 with a national sample of 1,600 persons plus some extensive samples of persons residing in five intercity rail corridors.

Publication of the data comes as Amtrak, the government-subsidized National Rail Passenger Corp., is facing the prospect of cutting back on services if federal financial aid is not expanded.

According to Harris, 56 percent of those persons polled would choose a car for trips over 100 miles, 28 percent would pick airplanes, 8 percent favor buses and 6 percent would choose trains. For travelers living in areas where train service is available, the percentage favoring trains increases to 9 percent, he said.

But 60 percent of the persons surveyed favor improvements in rail service (up from 54 percent in a 1972 Harris survey) and 51 percent favor more federal spending to achieve improved service.

From a list of nine proposed improvements in U.S. transportation, persons interviewed by the Harris team ranked auto safety first followed by better commuter mass transit and better intercity rail travel. New highways, new airports and fast airplanes were at the bottom of the list, Harris said.

"If any when energy shortages or the threat of energy shortages become more salient, the public mandate and demand for mass transportation and intercity trains will further intensify. The readiness of mass transportation to bear this greater loan will depend on the priorities the government sets today," he added, in an assessment of the sampling.

Generally good marks were given to Amtrak by those surveyed. The service's "performance rating" was 55 percent positive and 38 percent negative compared with the 1972 survey when 40 percent were positive and 42 percent negative.

In the Boston-Washington corridor, Amtrak got a 67 percent positive rating.