Backers of partial public financing of congressional election campaigns won a key test in the House Administration Committee yesterday as they defeated an attempt to extend public financing to primaries as well as general elections.

The attempt to include primaries was made by Rep. Mendel Davis (D-S.C.), long-time opponent of public financing.

Committee Chairman Frank Thompson (D-N.J.) ruled, on the advice of the House parliamentarian, that Davis' amendment was out of order, since the bill dealt only with general election campaigns.

Davis asked that the ruling be put to a committee vote and lost, 12 to 11, with the nine committee Republicans joining Davis and Rep. Robert Mollohan (D-W. Va.)

Davis argued that "equity and justice" demanded inclusion of primaries. But backers of public financing feel including primaries would virtually kill chances of passing the bill, since House Members from one-party districts or safe districts would look upon it as inviting primary opposition.

Rep. Bill Frenzel (R-Minn.) said there are at least 74 districts where victory in the primary is tantamount to election. He pointed out that primaries are covered in the law that made presidential elections publicly financed in part, and he said the issue was the "life's blood of the minority. . . . This is the most important amendment that will be raised on our behalf."

But Rep. John Burton (D-Calif.) disputed the number of single-party districts: "There is no longer a one-party South, and except in a few urban districts there are a few one-party districts. Democrats are now holding Republican seats and vice versa. It makes more sense to try this in a general election and see how it works."

In a concession to the opponents, Thompson indicated he would let the committee vote on letting the bill be opened to a primary-election amendment on the House Floor.

Thompson called yesterday's vote "a significant gain" for public financing, but refused to say it ensured a bill being voted out by the committee.

Republicans said the resort to parliamentary manuevers to prevent primaries from being included meant the Democrats still face considerable difficulty in getting a bill out.

Republicans, who see the bill as an "incumbent protection measure," said they would push for challenger-aid amendments to offset the $1.2 million in "perks" such as taxpayer-funded newsletters they say incumbents receive. One such amendment would let challengers spend 20 percent more than incumbents for mailings.

Under the bill the committee is marking up, contribution of $100 or less received during the election year would be matched with federal funds in increments of $10,000 up to $60,000.Those accepting federal funds would be subjected to an expenditure limit of $195,000 plus a cost-of-living percentage.

At least 80 percent of the contributions submitted for matching payments would have to come from individuals who reside in the state. If an opponent decided not to accept public funds, the expenditure ceiling would be lifted under certain conditions.