Maryland's congressional delegation has been been urged to help fight the Reagan administration's proposed changes in the Medicare program and to support a Vietnam veterans' volunteer group that wants to launch a statewide outreach program for unemployed and underemployed veterans.

In an appeal at a meeting of the delegation last Thursday, Matthew L. Tayback, the state's director on aging, warned that Maryland's 435,000 elderly face a 100 percent increase in the cost of their health insurance over the next few years if the proposed Medicare revisions are approved by Congress.

The proposals, opposed by the Maryland Commission on Aging, would require copayments from Medicare patients for hospital stays lasting from two to 11 days and would increase the typical monthly insurance premium from the current $11 a month to $30 a month over five years.

The average hospital stay is 11 days, according to Tayback, who said the copayment revision would increase out-of-pocket expenses for Medicare patients from $305 to $630 for a hospital stay.

Tayback said the proposals, called cost-containment efforts by the White House, would shift the burden of health care costs from the government to the elderly. He said health care providers "get off scot-free" under the proposals, when they should be sharing some of the increased costs of health care.

"It's placing the burden on people who work all their lives to build themselves up and most of whom live on the margin as it is," Sen. Paul S. Sarbanes (D-Md.) said.

Alexander Kramer, a senior citizen representative who testified before the delegation, said he was worried "one of these days it will be a choice of, 'Do we eat or do we get well?' "

Also seeking help from the delegation was the Maryland Vietnam Veterans Leadership Program, which wants to encourage businesses to fill their job openings with qualified Vietnam veterans, some 200,000 of whom live in the state. Unemployment among Vietnam veterans runs between 19 and 23 percent and hits black veterans the hardest, a group spokesman said.

"Our goal is to increase employer receptiveness to hiring Vietnam veterans," Mark Treanor, the group's chairman, told the delegation. "Government and the private sector working together can accomplish an awful lot."

Treanor and the group's executive director, David DeChant, have asked Maryland Gov. Harry Hughes and other state officials to publicize the "veterans-helping-veterans" group among business leaders and to help it obtain a portion of federal funds for veterans' projects.

The state is expected to receive $40 million to $60 million under the Job Training Partnership Act, which contains provisions for helping disabled veterans, Vietnam veterans and recently discharged veterans.

The group hopes to receive a grant of up to $250,000, according to DeChant, to set up a job bank and provide job-hunting assistance for Vietnam veterans still struggling for an economic footing.

"We make no statements about the war," DeChant said. "We don't have time for that debate and neither do the men who are unemployed."