House Republicans, angry because of a Democratic ploy they say would reduce a GOP advantage in campaign funds, attempted yesterday to hold as hostage the Democrats' major piece of economic legislation, the Humphrey-Hawkins employment bill.

As a House session to consider Humphrey-Hawkins began. Republicans demanded roll call after roll call "as a means of demonstrating our protest," Republican Whip Robert H.Michel (III.) said.

He said the intent was to slow down the markup of the election law bill in the House Administration Committee, where Republicans claim the campaign fund proposal is being "railroaded through."

In return, House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) threatened to keep the House in session "until 2 a.m." if necessary to finish the debate on the Humphrey-Hawkins bill, which would set a goal of reducing the unemployment rate from its present 6.3 per cent to 4 percent by 1983 and in general terms commit the government to getting there.

Republicans did succeed in delaying consideration of the procedural rule on Humphrey-Hawkins by 90 minutes by calling for votes on such matters as ending a quorum call and approving the previous day's record, and then tabling motion to reconsider that vote.

Each vote required Administration Committee members to come to the floor and delayed the markup of the election law bill.

Earlier in the day, House Republican leaders held a press conference to denounce the proposal as an "attempt to destroy the two-party system," as Minority Leader John J. Rhodes (Ariz.) put it.

The Democratic proposal would change the federal election law to reduce by 75 percent the amount of money national political parties could give House candidates. Since the Republican Party has raised three times as much money as the Democrats, Republicans consider it a "blatantly partisan move."

Rep. Guy Vander Jagt (R-Mich.), chairman of the Republican Congressional Campaign Committee, announced that all 147 House Republicans were protesting the move, which he called "the sleaziest, most partisan attempt in the history of the Congress to impose one-party rule on the United States."

But while Republican House leaders were holding a press conference to denounce the proposal, Rep. Charles E. Wiggins, a normally solemn, conservative Republican from California, decided to lighten up the Administration committee's markup session.

In the midst of the session, Wiggins suddenly produced a pretty green-and-white box tied with a pink ribbon and handed it to Chairman Frank Thompson Jr. (D-N.J.).

"Better put that in a bucket of water," Rep. Edward W. Pattison (D-N.J.), said.

In the box Thompson found a railroad engineer's cap - to help him "railroad the bill through," Wiggins said.

"This train might not stop at every station, but I hope you enjoy the ride," Thompson said.

Later, Rep. John Brademas (D-Ind.) produced a package for Wiggins containing a red Chinese peasant's cap to denote Wiggins as the "leader of the gang of four" Republicans spearheading the fight against the bill.

"Thank God you're quitting, man. You'd be dead in Orange County wearing that," Rep. John L. Burton (D-Calif.) told Wiggins, referring to his decision to retire.

The hat exchange was about the most significant action of the meeting, as Republicans attempted to offer amendment after amendment, and Democrats voted them down.

Democrats defend the reductions in what individuals, corporate and other political-action committees and parties can give candidates as an attempt to lower special-interest influence on House elections.

But Rhodes said Republican victories in four recent special elections for House seats have caused Democrats to want to change the rules.

The Senate has passed a bill that would change the election laws to increase party participation, particularly in presidential races where it was thought that public financing left the parties without a role. But the Senate bill does not make sweeping changes in the parties' spending limits. Rodes said Senate Republicans would "do all they can to oppose" the spending limitations in the House version.

House democrats hope to finish the election law bill in a few days and bring it to the floor around March 20.