A small army of volunteers from more than 100 churches and synagogues will be ringing doorbells in Montgomery County this Thanksgiving weekend in an effort to raise $100,000 to feed the hungry, both at home and abroad.

The wall separating church and state will be ignored on this occasion, as political and religious leaders combine their efforts in what will be the county's fourth annual Hunger Relief Drive.

Volunteers recruited from Protestant, Roman Catholic and Jewish congregations in the county will canvass residents in more than 100 precincts, asking for contributions to the hunger fund.

"The idea is catching on," said the Rev. Lon Dring, executive director of the interdenominational Community Ministry of Montgomery County, sponsoring organization for the effort. "People are taking hold with more vigor then they have in the past."

Last year's drive raised $82,000. Dring speculated that, with the increased interest from congregations indicated in preparations for this year's effort, this year's goal of $100,000 should be attainable.

The fund drive is the brainchild of Rep. Michael D. Barnes (D-Md.), who proposed it to the Community Ministry for implementation. Montgomery County Executive Charles W. Gilchrist and state Del. Constance A. Morella (R-Montgomery) have joined in promoting and participating in the drive.

One-third of the funds contributed will go to the Manna Food Center, the county's food bank; another third to the Capital Area Community Food Bank, and the remaining third will go overseas.

The amount earmarked for world hunger relief is distributed through Church World Service, UNICEF, Africare, the Catholic Relief Service and the American Jewish Joint Distribution Committee.

Because volunteers do all the work in the drive, there is no overhead and the total amount collected will go to aid hungry people, Dring said.

Although Montgomery County is one of the wealthiest in the nation, the number of persons in the county receiving emergency food aid is expected to show an increase from about 10,000 in 1980 to about 41,000 by the end of this year, Dring said.