Democrats on the House Administration Committee yesterday revealed a new set of campaign finance law amendements that would effectively wipe out the Republicans' fund-raising advantage in 1978 congressional elections.

The amedments - which would reduce by 75 percent the amount a political party could put into House campaigns - were denounced as "a partisan grab" by Common Cause and vehemently protested by Republican campaign officials.

Committee Chairman Frank Thompson Jr. (D-N.J.) said the amendments - on which he has scheduled a committee session Tuesday ar e just an "effort to cut down all around" on the cost of campaigns.

If enacted, the amendments would lower the ceiling on contributions and direct spending by national party committees in a House campaign from the existing $32,300 to $7,500.

That 4-to-1 reduction ratio, by coincidence, is exactly the same as the ratio between Republican and Democratic contributions in the past year to the congressional campaign committees. Republicans have collected $6.2 million, and the Democrats, $1.5 million.

Asked if the disparity was a factor in lowering the ceiling, Thompson said, "Of course, I never think like that."

But Fred Wertheimer, senior vice president of Common Cause and a lobbysist for public financing of congressional campaigns, said, "The Democrats have changed a campaign reform bill into a partisan grab and jeopardzed the entire legislative effort."

"This bill," he said, "is tilted toward the Democrats, based on a clear analysis of the money the Republicans have raised."

Steve Stockmeyer, executive director of the Republican Congressional Campaign Committee, said, "They (the Democrats) are paranoid, because we have our act together and they don't when it comes to fund-raising."

Republicans have captured four of the six Democratic-held House seats contested on special elections since November 1976 and in all of those contests have outspent the Democrats by wide margins.

Thompson cited this fact in explaining the action of his committee's Democrats, who caucused alone Thursday to draft the amendments which were made public late yesterday.

Both Wertheimer and Stockmeyer said that if Democratic effort was passed in the House, it would be blocked by a GOP fillibuster in the Senate - thus killing any changes in the law. The bill makes many simplifying amendments in reporting requirements and also reduces the ceiling on campaign spending by independent political action committees, which have mushroomed in the last two years.

Robert E. Moss, chief counsel of the House Administration Committee, denied that the bill was "antiparty or partisan." He said other changes in the law, removing spending ceilings on slate cards, campaign buttons and other material for volunteer distribution, might actually permit the parties to do more in campaigns than they do now.

But Stockmeyer said. "They're trying to shut down the influence of the national political parties, which, in our case, means 1.5 million of our contributors would lose their voice."