President Reagan's proposed 5 percent pay cut for federal employes would leave a typical single mother of two in Montgomery County $2,237 below the county's poverty level in 1986, according to a study released yesterday by Rep. Michael D. Barnes (D-Md.).

The study also found that the current salaries, even without the 5 percent cut, place typical single working mothers below the poverty level or the minimum level of need established by the Ad Hoc Committee of the Montgomery County Community Action Board.

"These findings dispel the popular notion that federal employes are overpaid," said Barnes, who released the study at a forum on women that he sponsored with Rep. Patricia Schroeder (D-Colo.).

The Reagan administration has proposed cutting federal pay 5 percent as part of its effort to reduce the federal deficit. The move was rejected last night by the Senate Budget Committee when it voted instead to freeze pay. The vote was the first step in a lengthy process.

In Montgomery, a typical single mother of two, working for the federal government in a clerical or secretarial job -- classified as GS 7, Step 4 -- makes $19,606. Her income after taxes is $15,528, and a 5 percent cut would leave her with a take-home salary of $14,858.

The 1985 poverty level in Montgomery is $16,359, according to the community board. Thus, this year without the cuts, her salary would be $831 below the poverty level. The federal poverty level, computed only for a family of four, is $10,183.

The study assumes that inflation in Montgomery will increase 4.5 percent next year. The expenses of a typical single mother of two would rise to $17,095, and a 5 percent pay cut would leave her $2,237 below the county's poverty level.

"Federal employes are not only behind their private sector counterparts, but as we see in the case of a single parent living in my district, they cannot adequately provide for their families on what the government pays," said Barnes.