Rep. Newton I. Steers (R-Md.) and Michael Barnes, his Democratic challenger for Montgomery County's Eighth District congressional seat, flailed away yesterday at each other's positions on everything from federal tax cuts to tuition tax credits for private school patrons.

The congressional contenders' contentiousness effectively stole the spotlight from the two candidates for governor of Maryland who appeared at the same forum at the Jewish Community Center in Rockville, and who sounded so much alike that one listener described them as "Siamese twins."

In contrast with Harry R. Hughes, his party's nominee for governor who began several answers by saying. "I agree" with his GOP opponent, former U.S. senator J. Glenn Beall, Barnes repeatedly identified "areas of fundamental disagreement" with Steers.

On taxes, Barnes said, "we could not be further apart." Barnes called the Kemp-Roth tax cutting plan, of which Steers was a cosponsor, "the worst idea" recent political history. Steers shot back that Barnes favored an even larger one-tie tax cut. "He's more inflationary," Steers said.

Barnes also criticized Steers' votein behalf of tuition tax credits, saying they would weaken public schools "that are often black" in favor of private ones" that are often white." Steers defended that vote saying parents of private schoolchildren "are doing us a favor" and deserve a financial break.

There was one set of issues on which the candidates did agree: both expressed strong support of Israel and of such Jewish causes as the right of Soviet Jews to emigrate. On these questions, they seemed bent on outpromising each oter.

After that brief moment of agreement, they returned to the divergent issues - including the question of whether Steers' ownership of certain stocks represents a conflict of interest which could affect his congressional votes.

When this question came up, Steers was ready for it. Confronted with Barnes' charges that Steers' ownership of an oil company's stock interferes with his work on a House energy committee, Steers produced a spray can of a product called WD-40, which he said is the only item manufactured by the oil company in which he owns stock.

"It doesn't produce oil, it use it," Steers said.

Barnes said later that Steers use of the oil can is part of an attempt by the freshman congressman to cloud issues raised by his energetic challenger.

A member of the audience asked Steers how the interests of Maryland's Eighth Congressional District were being represented when Steers abstained from voting on the banking committee because of his ownership of about $100,000 in a local savings and loan association. Steers responded that he abstained only three times out of 1,600 votes in the last two years.

"Short of giving away my stock, I don't know how to solve" those criticisms, said Steers, a millionaire who told the audience "I wish I had twice as much."

When the Jewish issues were raised , Steers pointed to two documents distributed in the lobby by campaign workers that he said documented 20 specific actions by him in behalf of Israel and 95 more in behalf of Soviet Jews.

Barnes pledged he would "never vote to sell offensive weapons" to Saudi Arabia, Egypt or any real or potential enemies of Israel.

During the 50-minute segment of the morning program devoted to the candidates for governor, Beall chided Hughes for the Democrat's public disagreement with his running mate, Sam Bogley, on the sensitive question of federal funding for abortions.

Hughes said that while Bogley personallt disagrees with spending tax money for abortions, his would-be lieutenant that "my policies will prevail" should Bogley have to take over the operation of state government.

Beall answered that he has known his running mate, Aris T. Allen, long time and "our views are compatible." Both Republicans favor abortion funding, and furthermore, Beall said, Allen is "competent enough to make his own decisions. He wouldn't have to wake up every morning and ask 'What would Glenn have done?'"