A U.S. government claim against the Soviet Union to compensate the families of the 61 Americans killed on Korean Air Lines Flight 007 almost certainly will be rejected by Moscow, legal experts and Reagan administration officials said yesterday.

The claim, which is being drawn up by State Department attorneys, will be forwarded to Soviet officials on Monday through normal diplomatic channels. But the Soviets are under no legal obligation to accept it, the experts said.

In case of disagreement over the terms, the matter could be referred to the International Court of Justice or the Permanent Court of Arbitration, both at The Hague. But that would require agreement by both sides, and the experts don't expect the Soviets to go along.

State Department attorneys yesterday explained the U.S. claim in Washington to families of the victims. Acting Secretary of State Lawrence S. Eagleburger expressed the department's condolences to the relatives.

Officials said the administration hasn't decided how much compensation to demand for each of the victims. The United States will first serve notice on the Soviets of the claim and then send on the details, they said.

There is no barrier to relatives' seeking damages from Korean Air Lines (which has announced that it will pay $75,000 for each of the dead) because the company's commercial operations in this country make it liable to claims in U.S. courts.

"Civil litigation is the appropriate avenue, and that has been tested," said Donald W. Malone, a 20-year veteran of aviation law. "But I'm not aware of a precedent for obtaining compensation for an international aircraft disaster through diplomatic procedures."

"There is no procedure to force the Russians to make compensation or even accept the claim," one international lawyer said. "There are no treaties in force that are relevant to the issue."

Experts said that the U.S. claim will accuse the Soviets of unlawfully shooting down a civilian passenger plane in violation of general international law and the so-called Chicago Convention on civil aviation.

Although they are pessimistic about a fast or positive Soviet response to the U.S. claim, lawyers noted that although it traditionally takes a long time to settle such demands, agreement is often reached when the political climate changes.

The forcing down of a U.S. transport plane by the Hungarians in the 1950s was settled two decades after the country rejected the American claim. The Bulgarians paid compensation to the Israelis for downing an airliner in 1955, and the Israelis compensated the Libyans for shooting down a passenger plane over the Sinai in 1973.

In a related development yesterday, the Mutual of Omaha Companies said that at least 16 passengers on Flight 007 were insured under its flight insurance policies, carrying a total value of $2 million.

A spokesman said that although the company's air travel policies contain an exclusion clause that voids losses resulting from declared or undeclared war it would not apply in this case.

"This was an accident, according to the terms of the policies," said the spokesman, Len J. Todl. "The exclusion clause will not apply." He said no claims have been filed.