The Maryland General Assembly convenes its 201st session Wednesday expecting to face 90 days of relative harmony on budget issues and a broad agenda of social concerns ranging from attempts to restrain the growth in medical care costs to the mandatory use of automobile seat belts.

The session is expected to be less contentious than last year's, when the 188 legislators wrangled over a number of politically explosive issues and feuded with Gov. Harry Hughes over his budget, but its results may have more immediate impact on Maryland's 4 million citizens.

"The controversies will be ones of philosophy rather than dollars," predicted Senate President Melvin A. Steinberg (D-Baltimore).

"I'm looking forward to a quiet three months," added House Speaker Benjamin L. Cardin (D-Baltimore).

If there is one issue that will dominate this session, it is the containment of health care costs. Hughes is expected to urge the General Assembly to adopt a long list of recommendations proposed by a task force that met throughout the fall to find ways to cut medical care costs.

Although Maryland, through tight regulation of hospitals, has succeeded in keeping the increase in health costs below the national average in recent years, prospective changes in federal Medicare payment rules dictate that the state do even better.

Since 1977, the federal government has allowed Maryland to set its own rates for Medicare and Medicaid patients as long as cost increases in the state have remained less than they are nationwide. That exemption from federal Medicare rates is the heart of the Maryland rate-setting system that guarantees equal access to hospital care regardless of financial circumstances.

But tougher requirements at the federal level have placed the federal exemption in jeopardy; if Maryland is to retain it, the state must cut medical costs even further. "We think we're going to lose the exemption ," said Cardin, "but we're going to take action that should make it very clear Maryland is acting in a responsible way to keep health care costs down."

To meet that goal, the health care task force has proposed some sweeping changes in the way the state regulates its hospitals and physicians, all designed to reduce a projected surplus of several thousand hospital beds, a particular problem in Baltimore. Among the proposals the legislature will consider are measures giving state regulators the authority to cap hospital revenues, close hospitals, halt hospital expansions and prevent doctors from purchasing expensive diagnostic equipment.

Hughes, in a recent interview, predicted that passage of the health-care package would not be "as difficult as some people think," because supporters represent a broad coalition that includes labor, business and consumers.

But many legislators, including Cardin and Steinberg, both of whom served on the task force, say it will take a major effort to push the proposals through. Legislators will be seeking to protect hospitals in their areas.

"We are ready to really knock some heads together in the legislature to get the health-care bills passed," promised Cardin. "And it will take that because the hospital lobby and the physicians' lobby have a lot of clout in Annapolis."

Less controversial, but equally important to one of Maryland's largest industries, will be legislation designed to reinvigorate the state's ailing thoroughbred racing tracks, which have suffered a steady decline in attendance and betting receipts. Hughes and the legislative leadership have been negotiating the specifics of what will be a joint proposal to make Maryland racing more competitive with other states, particularly New Jersey.

A key element of the racing bill will be reducing the share of the receipts taken by the state, currently set at 4.09 percent of total money wagered. The legislation will probably reduce the state's share to 0.5 percent and designate that much of the remainder be spent on purses and track improvements.

"The key to the success of this bill will be the legislature's willingness to change its attitude toward racing," said Del. Gerard F. Devlin (D-Prince George's), vice chairman of the House Ways and Means Committee, which will consider the legislation. "Traditionally we've looked at it as a revenue source for the state. We ought to be looking at it in terms of an industry that provides employment."

Gambling of another sort could well turn out to be the sleeper issue of the session. Recent events, including slot machine raids on the Eastern Shore and prosecutions involving club gambling elsewhere in the state, have convinced the legislative leadership that the state's gambling laws need an overhaul.

Meanwhile, with the state's economy enjoying the fruits of recovery, Hughes is expected to have no trouble funding his budget, which will total about $7 billion. And with a predicted surplus of about $47 million in the current fiscal year, there is even a little extra to go around.

"This will be the most normal budget I've seen since I became speaker," said Cardin. "The revenue is just what we want -- enough to do what we need to do and not enough to get us into trouble."

Two areas of the budget that could be contentious, however, are prison spending and the almost annual battle over the state's funding of abortions for poor women.

Hughes and the House leadership are heading for a confrontation over the future of the Maryland Penitentiary in Baltimore. The governor is expected to propose funds to renovate the aged facility, but there is strong sentiment in the House to plan for its replacement.

The governor, who in the past has tried unsuccessfully to liberalize the state's policy on Medicaid funding of abortions, is expected to seek no major change in the current regulations. Pro-choice advocates, who argue that current regulations have unfairly penalized the poor by restricting state-funded abortions, will push again for more lenient rules that last year passed the House but were stymied in the Senate.

Although Hughes' legislative program is considerably less grandiose than his program of a year ago, when he sought to increase local education aid and begin cleaning up the Chesapeake Bay, a major focus will be expanding social services, particularly for the young.

The heart of that effort will be the administration's so-called "youth initiative," conceived during an executive staff retreat on the Eastern Shore last summer. Included in that package of bills will be new and expanded programs in the areas of education, alcohol and drug abuse counseling, day care, prevention of child abuse and foster care.

Specifically, Hughes will seek to extend pre-kindergarten programs for disadvantaged 4-year-olds, strengthen child abuse laws by allowing background checks of teachers and day-care workers, create a youth employment project along the lines of the defunct CETA program, boost foster-care programs by $3 million to $4 million, expand day-care facilities and establish "family support centers."

Of more immediate concern to many Marylanders will be a number of attempts to pass legislation requiring motorists to wear seat belts and renewed efforts to crack down on drunk drivers. Among the latter is legislation that would make tavern owners responsible if patrons commit crimes while driving drunk.

Other issues to watch include:

* Interstate banking. A year after rebuffing Citicorp's effort to open branch banks in Maryland, the legislature is expected to approve legislation that could permit such interstate banking by the year 1990.

* Education. There is considerable support for giving Baltimore $7.5 million this year in supplemental aid, despite the fact that last year's program was supposed to be the last.

* Coal slurry pipeline. Although a special legislative committee has recommended taking no action that would open the door for electric utilities to construct a pipeline to transport coal from West Virginia to port facilities on the Chesapeake, the utilities may push ahead anyway in their bid to reduce the cost of shipping coal by rail.

Looking over this year's legislative agenda, much of which has emerged from interim study commissions with broad backing, Steinberg predicts a "good, productive session that will be much easier than 1984."

But in Annapolis, conventional wisdom has a way of falling apart once the opening gavel falls, and some legislators are forecasting stormy times ahead.

One of them is State Sen. Howard A. Denis (R-Montgomery). "It appears that everything has been resolved, and the session will be an afterthought," said Denis. "But I think it will be raucous, chaotic and undisciplined."

His reason? The election of 1986, in which the governorship, one U.S. Senate seat and the House speaker's position will be contested by a cast of key players in Annapolis, many of whom will be jockeying for position.