Leaders of the nation's interstate bus transportation companies yesterday warned that their survival is threatened by higher costs and government subsidies to Amtrak, the national rail passenger corporation.

At an informal hearing before members of the Interstate Commerce Commission, several spokesmen said higher fares would be proposed in the near future. They asked the regulatory agency to ack quickly on the proposals, and some sources said the industry may seek some form of federal subsidy for money-losing bus services.

"This industry is in trouble," said Fred Currey, chairman of Trailways, a subsidiary of Holidary Inns. "I feel that the bus industry is fighting for its health - if not for its life."

Currey contended that the ICC has not approved fare increases prposed in the past and has been inattentive to a worsenig industry plight. With declining profits, bus companies lack capital to replace buses and renovate terminals, he added.

At the same time, low-income groups, minorities, senior citizens and young people depend on buses for relatively inexpenseive transportation, Currey noted.

He charged the ICC had discouraged "fair" competitions among various forms of transportation because bus firms were not allowed to reduce fares - even on an experimental basis - without "jeopardizing" future fare increases. He called on the agency to authorize "rate experimentation."

According to the National Association of Motor Bus Owners revenues for 82 major bus lines rose by 4.7 per cent last year to $992 million, but expenses climbed 6.6 per cent and overall profits fell to $34 million from $42 million in 1975.

Intercity bus travel also declined slightly last year at 25.3 billion passenger miles.