The government's Medicare advisory panel voted yesterday to recommend major improvements in program benefits, to be financed by a sizable increase in the monthly premiums beneficiaries must pay if they want doctor as well as hospital insurance.

The recommendations come from the Social Security advisory council that the secretary of Health and Human Services is required to name every four years to study the system. This year it is headed by Dr. Otis R. Bowen, former Republican governor of Indiana, and is focusing on Medicare, which is in serious financial trouble.

Under the proposal approved yesterday, Medicare patients would be eligible for up to 365 days of hospital care each year after paying an initial $350 to cover the first stay and one additional $350 payment if any additional stays were required. This is much more generous than existing coverage which provides for the initial payment and then only 59 days of free care and charges substantial amounts beyond that.

In addition out-of-pocket costs for each person who enrolled in the optional doctor insurance (Part B) program for doctor bills would be limited to $200 a year.

To pay for these improvements the annual charge for enrollment in Part B, which is now $146.40 a year and will rise automatically to $176.40 in 1984, would be increased an additional $244.50 for a total of $420.90.

The added funds would not only cover the costs of the added hospital and doctor benefits but raise an additional $2.4 billion in the first year to help meet Medicare's rising deficit which is expected to make the hospital trust fund insolvent by 1990 unless something is done.

The commission has estimated that Medicare's hospital trust fund will spend $200 billion to $400 billion more than it takes in by 1995 unless new funds are found.

Bowen and other members of the panel, using data developed by their staff and actuaries, said the new benefits would generally make it unnecessary for Medicare beneficiaries to purchase commercial "medigap" insurance policies to cover what Medicare does not. About 65 percent of all Medicare beneficiaries buy such medigap insurance and pay anywhere from $300 to more than $800 a year for it.

Any amendments to Medicare would have to be approved first by the White House, then by Congress--and these would almost certainly face opposition because of the increase in the premium.

Stan Arnold, secretary-treasurer of the Michigan Building Trades Council, foreshadowed such opposition yesterday when he said many low- and middle-income elderly beneficiaries would find it impossible to pay the additional premium, even if it did buy extra coverage. He insisted that the staff bring back recommendations on ways low-income people could be helped to meet these added costs.