The State Department yesterday made public a 124-page collection of "reports on the use of chemical weapons in Afghanistan, Laos and Kampuchea" (Cambodia) and indicated it now had "very fragmentary" reports that chemical warfare was also being waged in Ethiopia.

The report is meant both to buttress U.S. contentions that there is enough circumstantial evidence of gas warfare by Soviet or Soviet-backed regimes to warrant an international investigation and to provide other interested countries with the material gathered thus far.

The report is mostly an account of interviews with refugees from these countries plus numerous other newspaper and magazine articles where these allegations have been reported.

Officials, for example, called attention to an article published this week in the Dutch magazine "Nieuwsnet" by reporter Bernd De Bruin, who claims to have spent five weeks in Afghanistan. De Bruin claims the Soviets use tactics that combine bombing first with some sort of gas and then with napalm to eliminate traces of the chemical.

The report was distributed to reporters yesterday, and officials from State and intelligence agencies were on hand to answer questions though, under the rules of the briefing, they cannot be identified by name.

Officials stressed that the United States has not made formal charges against the Soviets. Rather, it has made numerous statement's in international bodies calling for a fact-finding commission, thus far with no takers. "No international organization considers this to be their baby, unfortunately," one official said.

The United States is now consulting with other countries prior to a decision about raising it in the United Nations, and this new report is meant to set the stage for whatever happens next.

The Soviet, Laotian and Vietnamese governments have all denied using gas warfare and there is no indication any country would allow fact-finders in if a commission were established.

The U.S. government concludes fro m the evidence available thus far:

"In Afghanistan, we regard it as highly likely that Soviet forces have used some form of chemical agents in their efforts to suppress Afghan resistance. And there are a number of refugee reports that the Soviets have used incapacitant and lethal chemical agents."

"In Laos, the information at our disposal supports the conclusion that Vietnames and Lao forces probably have used lethal chemical agents against the Hmong tribesmen for several years. Our estimates based on interviews of Hmong refugees are that approximately 700-1,000, persons may have died as a result of the use of chemical agents."

"In Kampuchea, the evidence is somewhat less substantial," the report says, though it cites some reports from defecting Vietnamese soldiers who had been in Cambodia. "In sum, the U.S. believes there is enough circumstantial evidence to warrant serious concern and a careful examination. . . ."

The officials gave no further details of possible use in Ethiopia, a Marxist country fighting a lingering battle with neighboring Somalia and beset with an internal secessionist movement in Eritrea province.

The preliminary concern, officials said, was the potential for a continuation of the pattern of chemical warfare which began in Laos in 1974 and, in their view, spread through to Cambodia and Afghanistan.