WASHINGTON (AP) _ Standing in for Lt. Col. Oliver L. North, dozens of House Republicans displayed for television cameras Thursday their version of the pro-Contra slide show North was barred from showing last week when he testified before the congressional Iran-Contra committees.

Ready for that move, Democratic foes of continued U.S. weapons aid to the Contra rebels counterattacked by displaying large-format photos of wounded Nicaraguan men, women and children they contended were innocent victims of Contra guerrilla attacks on innocent Nicaraguan civilians.

The competing exhibitions of politically barbed visual aids marked the unofficial but impassioned opening of this year's debate over whether to approve a new $100 million installment of lethal aid to the Contras.

The debate that resulted, spit out under the rules of the House in two hours of one-minute speeches, was marked by an exchange of complaints, accusations and insults between the two sides.

Contra supporters accused opponents of swallowing ''communist propaganda'' and being ''soft in the head.''

The Contra backers were accused in turn of supporting a military force that commits atrocities.

In his congressional testimony last week, North, a former National Security Council aide, was permitted to verbally describe each of the slides he had used in pro-Contra presentations in 1985 and 1986. His slide show was put together to provide the warmup for appeals by others for private donations to the Contra cause.

Two men, Carl R. ''Spitz'' Channell and public relations executive Richard Miller, who followed North's slide-show presentation to collect funds for the Contras, have pleaded guilty to charges they illegally used a tax-exempt foundation in their efforts. Both men named North as a co-conspirator.

North was not permitted to show the actual slides. Senate Chairman Daniel K. Inouye, D-Hawaii, said that for security reasons the lights in the Senate Caucus Room could not be lowered to permit them to be seen.

So the slides were converted to photographic enlargements for conservatives to use on the House floor Thursday in a sort of political show and tell.

They showed charts, maps, quotations and photographs, all illustrating the theme that Nicaragua is becoming a forward Soviet military base in the Western Hemisphere.

The competing presentation mounted by opponents of Contra aid was intended to support assertions that the rebels have committed atrocities against noncombatant civilians in their fight against Nicaragua's pro-Marxist Sandinista leadership.

''We're trying to bring this down to a very human level,'' said Rep. Mary Rose Oakar, D-Ohio, as she showed a photograph of a wounded Nicaraguan woman. ''We're talking about human beings, not charts. I think the people of Nicaragua will never side with our philosophy if we keep using our tax dollars in this manner.''

But conservative House members accused their colleagues, and liberal church groups, of blindly accepting Sandinista propaganda.

''It is communist propaganda channeled through church groups and by unwitting members of the House,'' said Rep. Dan Burton, R-Ind. ''... I hope it's unwitting.''

''People who say all of the information we have is espoused by the communist party are absolutely ridiculous,'' said Rep. Bill Hefner, D-N.C.

Rep. Dan Coats, R-Ind., said supporting the Contras is good policy, ''not because the Contras are the most embraceable people in the world, but because they are the most viable alternative to keep the Sandinistas tied down.''

Opponents of Contra aid are ''squishy soft,'' said Rep. Donald E. Lukens, R-Ohio. ''Are they just soft in the head or do they really believe communists in Nicaragua will just go away?''

''They (the Contras) do not advance democratic principles by killing unarmed peasants,'' Rep. Tony Hall, D-Ohio, said on the other hand. ''These are not the kind of people are country should be supporting.''

Rep. Duncan Hunter, R-Calif., said ''not a single member of the Democratic side got up'' to dispute that the North photographs show military bases, ports and airstrips, tanks, helicopter gunships, weapons and Soviet warships ''13 miles off the coast of Louisiana.''

Rep. Robert Mrazek, D-N.Y., showing a photograph of a Nicaraguan mother and child he said were victims of a Contra atrocity, told the House: ''Atrocities are atrocities no matter who commits them. It is hard for Americans to understand who the good guys are and who the bad guys are in that region.''

The official debate over renewing Contra aid will begin sometime this fall.