The Virginia Senate approved legislation today that would require drivers and front-seat passengers in motor vehicles to wear seat belts, a measure that has received strong support from Gov. Gerald L. Baliles.

The proposed law, which will be returned to the House to work out differences in the House and Senate versions, would become effective Jan. 1, 1987. Persons convicted of violating the law would be subject to a $25 fine.

"We can save 300 to 400 lives a year with this bill," said Sen. Daniel W. Bird Jr. (D-Wythe), a former opponent of the law who switched his position after he and his wife Barbara were in a serious car accident last year. Bird credits a seat belt with saving his wife's life.

The Senate, which in past years has killed the mandatory seat belt measure in committee, approved the bill 22 to 17 today over the objections of legislators who said government should not interfere with personal freedom.

"It infringes somewhat on my freedom," said Sen. John H. Chichester (R-Stafford), who voted against the measure. "If I don't do it wear a seat belt it harms no one but me."

The Senate version of the measure eliminated a House amendment that would have allowed police to charge a motorist with failure to wear a belt only if the motorist had been stopped for some other infraction. That key difference is expected to be addressed by the House.

The seat belt bill has been the target of intense lobbying and emotionally charged public hearings throughout this legislative session.

Baliles told legislators in his inaugural address in January that he would sign a mandatory seat belt law. He and members of his staff have been lobbying forcefully for passage of the measure.

The issue provoked more than an hour of heated debate today as proponents waved lists of statistics and opponents argued for personal freedom.

"I'm convinced they do save lives," said Sen. Frank W. Nolen (D-Augusta). "But I don't think it's right that people have to wear them if they don't want to."

National safety specialists have said that regular use of seat belts by motorists could save nearly 10,000 lives annually and prevent 327,000 serious injuries.

However, even proponents of the seat belt measure argued that the bill's enforcement provision -- a $25 civil penalty for violations -- was weak.

In addition, motorists fined for violating the law would not be required to pay court costs as mandated in other traffic offenses. And, a motorist's failure to wear a safety belt could not be used as evidence in civil actions resulting from automobile accidents.

The bill would exempt drivers of taxicabs, rural mail and newspaper carriers, law enforcement officers transporting persons in custody and anyone who receives a doctor's certificate stating that wearing a seat belt would be harmful.

State law already requires that passengers under age 4 be placed in safety seats or harnesses.

Legislatures throughout the nation are considering mandatory seat belt laws under threats that the federal government will require all American automobiles to have air bags unless states representing two-thirds of the country's population enact seat belt laws by April 1, 1987.

Some senators argued yesterday that automobile manufacturers are pushing mandatory seat belt laws to avoid requirements that they install air bags in American cars and trucks. Sixteen states and the District have approved seat belt laws; a measure is pending in the Maryland General Assembly.

Senators voting in favor of the mandatory seat belt law:

Howard P. Anderson (D-Halifax), Hunter B. Andrews (D-Hampton), Peter K. Babalas (D-Norfolk), Daniel W. Bird Jr. (D-Wise), John C. Buchanan (D-Wise), Charles J. Colgan (D-Prince William), Clive L. DuVal II (D-Fairfax), William E. Fears (D-Accomack), Joseph V. Gartlan Jr. (D-Fairfax), Elmon T. Gray (D-Sussex), Clarence A. Holland (D-Virginia Beach), Edward M. Holland (D-Arlington), Benjamin Lambert (D-Richmond), J. Granger MacFarlane (D-Roanoke), Madison E. Marye (D-Montgomery), Thomas J. Michie Jr. (D-Albemarle), Wiley F. Mitchell Jr. (R-Alexandria), Robert E. Russell (R-Chesterfield), Elliot S. Schewel (D-Lynchburg), Robert C. Scott (D-Newport News), Charles L. Waddell (D-Loudoun) and Stanley C. Walker (D-Norfolk.)

Senators opposed:

W. Onico Barker (R-Danville), A. Joe Canada Jr. (R-Virginia Beach), John H. Chichester (R-Stafford), Elmo G. Cross Jr. (D-Hanover), Dudley J. Emick Jr. (D-Botetourt), Virgil H. Goode Jr. (D-Franklin), Richard J. Holland (D-Isle of Wight), R. Edward Houck (D-Spotsylvania), Johnny S. Joannou (D-Portsmouth), James P. Jones (D-Washington), Kevin G. Miller (R-Rockingham), Frank W. Nolen (D-Augusta), William T. Parker (D-Chesapeake), William F. Parkerson Jr. (D-Henrico), John W. Russell (R-Fairfax City), Richard L. Saslaw (D-Fairfax) and William A. Truban (R-Shenandoah).