Alan S. Boyd will leave Amtrak Wednesday after four years and a month as its chief executive officer, confident that there's been a significant improvement in the nation's rail passenger service during his tenure and optimistic about its future.

"I think that rail passenger operations are going to grow in this country," Boyd said in a farewell interview. "I don't think the growth will be dramatic--like a rocket taking off to the moon--but I think it will be steady and sustained."

Although Amtrak will be able to cover the costs of some trains--especially on high-density corridors--from passenger fares, Boyd doesn't think a nationwide system can be self-sustaining. With just 220 trains a day, there isn't enough volume to cover overhead, he said.

Continuing reform of its labor contracts and the development of its assets in a diversification program, though, should allow Amtrak to generate internally all the funds for its capital requirements by the end of the decade, Boyd predicted.

This year, Amtrak will recover at least 50 percent of its costs with passenger fares, up from 42 percent last year, Boyd said. Over Amtrak's 11-year life, it has consumed more than $5 billion in federal subsidies; right now, the subsidy averages about $35 a passenger.

Although he has worked to see the subsidy diminished, Boyd says he has no philosophical objection to the subsidy. "I don't see any particular reason why rail passenger service should operate without public support," he said.

"We have any number of programs in this country which deal with the redistribution of wealth in the public interest. Subsidy represents a judgment by the government that the expenditure of this money is in the public interest."

Since June 1, 1978, when Boyd climbed aboard, the National Rail Passenger Corp.--Amtrak's full name--has changed significantly:

A national network is in place; new or totally rebuilt equipment has replaced all the dilapidated equipment Amtrak started with; ridership grew until the economy turned sour and New York Air cut into its Washington-New York corridor traffic; a new computerized reservations system is in place and working well; trains are faster; on-time performance is improved; the rail bed is smoother; revenues are covering a greater portion of costs; and some trains are even sold out.

"Right now it's kind of hard to remember but, in 1978, our on-board service employes were spending their trips apologizing for the breakdowns," Boyd recalled. "The beds wouldn't work. There was no water. The toilets didn't work; the air conditioning didn't work; the heat didn't work; the lights didn't work.

"That's all behind us now," he said. The replacement of the old equipment in the past four years is not something he can take credit for, Boyd said, because the new equipment was ordered by his predecessor. The change was important because of its impact on the public and because of its impact on the attitudes of the employes, he said.

Boyd was willing to take some credit, though, for focusing the efforts of the rail's management team, some whom he brought to Amtrak.

"Everybody is working for the same goals--the company goals--which is improved passenger service," he said. In particular, the operating and maintenance people now take it "as an article of faith" that their departments are service departments to meet the needs of the marketing department.

"This represents an enormous change in the attitude in the railroad industry generally. The operating people have always felt that they ran trains for their benefit, and if the marketing people could get some traffic, well and good."

Boyd says he has two disappointments: During his tenure, he was not able to obtain some kind of permanent or long-term funding in order to avoid annual appropriations--and provide planning stability--and he wasn't able to raise salary levels for top officers, which he called "egregiously bad."

Boyd, 59, has been involved in transportation, mostly in the public sector, all his adult life. After a stint in the Air Force, he served as a member and then chairman of the Florida Railroad and Public Utilities Commission, a member and then chairman of the Civil Aeronautics Board, undersecretary of Commerce for transportation, and then became the nation's first secretary of Transportation in 1967.

When the administration changed in 1969, he joined the Illinois Central Railroad as president and stayed in the private sector until asked by President Carter to be chief negotiator on a U.S.-United Kingdom aviation agreement. The Amtrak assignment was next.

Boyd is expected to be named chairman and president of Airbus Industrie of North America, the U.S. marketing arm of the European aircraft manufacturer. He wouldn't comment on his future employment, noting that the key element in his decision to leave Amtrak was his feeling that he had accomplished essentially what he wanted to, and that he probably wouldn't be able to do much about the couple of things he hadn't been able to accomplish.

"I've been running--if I can use that term advisedly--very large organizations for a long time," he said. "And it's challenging, it's pleasant and it's wearing.

"I feel a need to be in an environment where I'm getting fairly close to an assistant, a secretary, and nobody else," Boyd said.