Maryland's congressional delegation told the General Assembly leadership yesterday that if President Reagan's budget is enacted, the state may have to take on additional programs or drastically cut services.

"We face a dramatic alteration of the process by which government is carried on in this country," said Sen. Charles McC. Mathias (R). "There will be a major shift of responsibility out of Washington and into Annapolis."

If Congress cuts funding for Amtrak and the Small Business Administration, two moves proposed by Reagan, Mathias said, "that would mean the legislature would have to consider whether it wants to develop programs on the state level."

Failure of the state to allocate money for the federally slashed programs would leave "a gap in service that the legislature would have to think about," Mathias said.

The warning, coming at what was billed as an unprecedented dialogue between the state's legislative leaders and the congressional delegation, did not come as a surprise to state officials.

"We're facing some very difficult times in the state of Maryland and in this country," said House Speaker Benjamin Cardin, who joined in asking for "close cooperation" between Maryland's state and national political leaders.

Cardin and other state leaders harped on the harsh impact of the federal budget on Maryland, which they said has a prudent fiscal plan and is ahead of other "flabby" states that receive a greater percentage of funds from the federal Treasury.

Reagan's proposed budget will cost Maryland about $100 million in aid, including $9.9 million in education, $12.7 million in employment and training, $18.8 million in health and mental hygiene and a whopping $26.1 million in aid to local governments.

Those figures also do not include a $73.6 million cut in highway and mass transit aid, and the end of federal revenue sharing, which will cost the state about $71 million.