Maryland Attorney General Stephen H. Sachs yesterday issued an opinion which, if upheld in court, would strike down the annual property tax exemption granted to Burning Tree Club, the last all-male golfing bastion in the Washington area.

Today, Sachs plans to file suit in Montgomery County Circuit Court seeking a declaratory judgment that would remove the tax exemption because the club does not admit women.

"I'm confident the courts will agree with our findings," Sachs said yesterday, adding that he hopes the matter may be resolved as early as next month.

Assistant club manager Gordon Jones said that club officials will have no comment on the opinion. Members of the club, which charges a $12,000 initiation fee to its 600 members and $1,700 in annual dues, have said in the past that eliminating the exemption might turn Burning Tree into "a rich man's club." This year, Burning Tree was required to pay only $13,000 of the $165,000 it was assessed in property taxes by the county and state.

Sachs said in his opinion that the state law granting Burning Tree its exemption as a "single-sex club," is unconstitutional under provisions of the state's Equal Rights Amendment, which was passed in 1972.

"The central issue is not whether a single-sex country club in Maryland may continue to close its doors to one sex," Sachs wrote. "The issue is whether Maryland's country club tax preference scheme unconstitutionally involves the state in subsidizing sex discrimination."

Burning Tree is one of many country clubs in the state that receives a property tax exemption under "open space" provisions in the state law by agreeing not to develop the land on which the golf club is built. Burning Tree is the only single-sex club receiving the tax break currently.

The argument of state subsidization was made earlier this year by State Sen. Stewart Bainum Jr. (D-Montgomery), the chief sponsor of a bill that would have eliminated the exemption for Burning Tree. After Bainum's bill was killed by parliamentary maneuvering in the final minutes of the 1983 General Assembly, he and Sachs independently began researching the legal questions raised by the issue.

Last week, Bainum formally requested an opinion from Sachs. Upon delivery yesterday Bainum said, "I'm delighted."

"During the three years I've sponsored the bill it's been tough getting public officials outside the General Assembly to support us. Montgomery County Executive Charles W. Gilchrist was always the exception and this year Sachs and Gov. Harry Hughes supported it."

Bainum said that he and members of a women's legal defense fund will file a separate, joint lawsuit against both Burning Tree and the state, and their suit and Sachs' may be consolidated.

During its 60 years of existence Burning Tree has become known as the "Club of Presidents," because many presidents, members of the Supreme Court and Congress, have been members. President Reagan does not belong to Burning Tree. Women are not allowed on the grounds of the club except for one week before Christmas, when they may enter the club's pro shop to buy Christmas presents.

Burning Tree's special tax status was established in 1978 during the administration of then- Attorney General Francis B. Burch, according to Sachs' opinion. In a letter written by the late John F. Oster, then a deputy attorney general, Burning Tree was granted special status as a "single-purpose" club and therefore was allowed to keep its tax exemption. Burning Tree is the only club ever granted such status by the state.

Oster wrote then, "The only way the club could be operated to serve both sexes would be by building a substantial addition to the clubhouse which would have the affect of requiring major changes in the location of the first tee, the ninth tee and the 18th green."

Sachs said that whether fraternal organizations such as the Elks and the Moose should lose their tax exemptions because of discriminatory practices is a separate issue. Bainum has requested an opinion on the legality of tax exemptions those organizations receive.