Professional income tax preparers such as H&R Block may be responsible for about one-third of the $1-checkoff contributions that go into financing Presidential campaigns, House Minority Whip Robert H. Michel (R-Ill.) told a House committee yesterday.

Treasury Department figures show that 29 percent of the nation's taxpayers check off the box on their income tax forms indicating that they want to give $1 of their taxes to finance presidential campaigns.

"Based on information from the Treasury, about 42 percent of all tax payers go to professional income tax preparers to do their figuring. According to previous testimony [from the Federal Election Commission], we learned that most of those professional organizations simply take it upon themselves to check off the $1 presidential campaign contribution for their clients," Michel said.

He estimated, therefore, about one-third or 8.6 percent of the 29 percent who check off "may not even be aware they are making the contribution."

The Republican whip testified at a House Administration Committee hearing on a bill that would provide partial public financing for House races.

Michel argued that in fact the 70 percent of the people who do not check off should be looked upon as being against publicly financing presidential campaigns, and would be against H.R. 1, the bill the Administration Committee is considering to extend public financing to House races.

"This bill shouldn't be H.R. 1, it should be H & R 1, appropriately christened in honor of one of the firms which has apparently kept the checkoff system afloat this long," Michel said.

Michel was one of several Republican leaders who testified yesterday against the bill, while a coaliton of Democratic and Republican House Democratic and Republican House members, including Republicans John Anderson (ill.) and Barber Conable (N.Y.) and Democrats Abner Mikva (Ill.) and Morris Udall (Ariz.), testified for it.

Udall, who was an unsuccessful presidential candidate in 1976, said that campaign, the first ever publicly financed, was the "cleanest election we ever had, the best election we ever had."

Conable denied the often-repeated charge that the bill would benefit incumbents. He said of the challengers who best incumbents in 1978 House races, only four of the 19 managed to raise and spend more than the ceiling in the bill of about $200,000. Conable said the bill would give challengers access to money and limit special-interest money given to incumbents.

Anderson said in the 1978 elections, incumbents got $30,000 on the average from business and labor political action committees while challengers got $12,500. Anderson said the growth of special-interest money is alarming and it is "becoming a system of purchasing access and the expectation of legislative favors, and it is time for a change."

Meanwhile, a group of 25 organizations, including Common Cause, the United Auto Workers, the National Farmers Organization and the National Urban League signed a letter to House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) asking for quick action on the bill.

Proposals for public financing have come up in Congress for the past several years but never passed the House. The battle this year is particularly intense, as supporters push to get a bill to the floor far enough away from the next election to prevent that clouding the issue, but close enough to the last election to keep the increased special-interest spending fresh in members' minds.

House Democratic leaders have made the bill a priority, but at best it is given a 50-50 chance. Though the House Administration Committee hearings seem to indicate there is a majority against the bill, its supporters claim they will be able to muster enough votes to get it to the floor.

"The battle lines are clearly being drawn," Common Cause Vice President Fred Wertneimer said. "I think because we are getting close to having enough votes is why we are generating such intense opposition this time."

The bill would cover general elections only, beginning in 1980, and would match small, private contributions of $100 or less with up to $60,000 in public funds. An overall spending ceiling of about $213,000 would be applied and candidates would be prohibited from using more than $25,000 in personal funds.