The Maryland Senate today approved without debate an $8.15 billion budget for fiscal 1987, which begins July 1.

The unusually harmonious deliberations yielded $46 million in cuts from the $8.2 billion measure originally submitted by Gov. Harry Hughes. The senators said that a portion of the funds cut from the budget will be designated for a special reserve fund established in response to the state's savings and loan crisis.

The measure now goes to the House of Delegates for review. Both houses must agree on the state's spending plan by March 31.

Among the cuts recommended by the Budget and Taxation Committee and upheld by the full body were:

*$10.8 million from the Department of Health and Mental Hygiene, including heavy revisions to the budget of the troubled Juvenile Services Administration, which supervises programs for juvenile offenders.

*$14 million from the Department of Human Resources, including a reduction in the number of new case workers, and $7.7 million in funds to insulate low-income households. The committee reasoned that the funds could be replaced by revenues expected from a successful lawsuit against Exxon Corp. But Attorney General Stephen H. Sachs ruled this week that the state can use those funds only to beef up programs, not to avoid spending state dollars.

*$500,000 from the Employment and Training Department to eliminate a youth training program initiated last year in an effort to deter youths from dropping out of high school. The committee said the program results did not justify the expense.

The Senate also acted to restrict the expenditure of funds for the governor's $400,000 program aimed at combating teen-age pregnancy until the budget committees have approved guidelines for the expenditure.

In other action:

*The Senate gave preliminary approval without discussion to a package of bills aimed at curbing skyrocketing medical malpractice insurance premiums. The bills, which would mainly decrease the number and cost of lawsuits filed against doctors, have been the subject of intense lobbying by doctors, who favor them, and lawyers, who are strongly opposed.

*Legislators from Baltimore and Baltimore County defeated efforts to overturn laws forbidding Sunday store openings in much of the Baltimore area, assuring that the so-called blue laws will stay in place for at least another year.