Cambodia is attacking its Indochinese Communist neighbors, Vietnam and Laos, as well as Thailand. Thai Prime Minister Thanin Kraivichien charged today.

The most serious clashes, Thanin told reporters here, are taking place along the Cambodian-Vietnamese frontier. "They even have planes bombing on both sides," the premier said, adding that "the conflict between Cambodia and Vietnam on the border dispute is far worse than the Cambodian-Thai border," the scene of several recent clashes.

Reports of clashes between Cambodia and Vietnam have filtered out of Indochina since shortly after the end of the war against U.S.-backed forces in the region in 1975, but Thanin's claim, of fighting along the Cambodian-Laotian border was the first Indochina watchers here could recall.

A Bangkok-based diplomat from a nonaligned country said recently that some 200 Vietnamese troops were killed in a fierce battle with Cambodian forces near the so-called Parrot's Beak area of Southern Cambodia last month.

The French newspaper Le Monde reported this week that sporadic fighting with artillery and aircraft was taking place in the Hatien area of southern Vietnam, near the Gulf of Siam.

The Cambodian Communists are understood to have only a handful of outdated U.S. built T-28 propeller fighters, taken over from the defeated air force of former Cambodian President Lon Nol. According to intelligence sources, Chinese pilots are instructing the inexperienced Cambodians to fly the small aircraft.

Vietnam has a substantial Air Force, equipped with Soviet-built Mig 19s and Migs 21s.

Thanin's information, presumably based on U.S. intelligence reports, indicated that the fighting on the Vietnamese and Laotian borders with Cambodia is continuing. Asked if he was referring to reports of previous battles or whether the fighting is going on at the moment, the premier replied,"actually, at the moment."

Thanin, who is regarded even by some members of the military junta that supports his government as an inflexible anti-Communist, suggested that the Cambodians were attacking all their neighbors in an attempt to divert the attention of Cambodians from domestic crises.

At least 27 Thais were slain in attacks on two border towns 85 miles east of Bangkok this week. Last month, 25 were killed in a similar assault near the border town of Aranyaprathet. Last Janauary, 30 villagers were slain in an especially brutal attack.

Thanin's contention that the Cambodian Communist regime was creating border disturbances in order to distract the nation's population appears to contradict reports from Cambodian refugees reaching sanctuaries in Thailand.

According to many of these refugees, there are no news media in Cambodia and people are kept totally uninformed about events in their country and elsewhere.

Some followers of cambodian developments believe the incidents on the Thai frontier were provoked by locl Cambodian commanders in need of food and supplies for their units. Another theory is that a recent crackdown by Thai authorities on smuggling across the border dried up a source of supply for the Cambodians and that they were forced to retaliate.

Until now. Thailand has responded to the attacks by defending what it considers its own territory along the long-disputed. Thai-Cambodian frontier. Thanin said in reply to a question, however, that if the attacks continue, he might order a counterattack into Cambodian territory.

Thanin made his remarks at a news conference after the end of a two-day meeting of leaders of the five-member Association of Southeast Asian Nations-Thailand, Malaysia, Singapore, Indonesia and the Philippines.

Except for Thailand, and to a lesser extent Singapore, the ASEAN countries took a conciliatory atttitude toward the three Indochinese states.