LISBON, Portugal (AP) _ Angola's Marxist government claimed Thursday that its soldiers killed 270 guerrillas last week, and the U.S.-supported rebels said they shot down a government supply plane, killing all 25 people aboard.

In France, the Foreign Ministry announced that a French technician abducted by Angolan rebels died during a long, rugged march with his captors through the southern African country.

Angola's state airline confirmed a plane was lost and was investigating the cause of the crash. The other claims could not immediately be verified. The rebels have been fighting to share power with Luanda's Soviet-backed government since shortly after Angola gained independence from Portugal in 1975.

Angola's state news agency ANGOP said 270 guerrillas of Jonas Savimbi's National Union for the Total Independence of Angola, or UNITA, were killed in fighting in six provinces in central and southern provinces last week. The report said 37 government soldiers were killed and 63 wounded in the fighting.

The rebels released a statement in Lisbon saying they shot down a government supply plane Tuesday as it flew from Huambo to Cuito, the capital of central Bie province. They said all 25 people on the plane died.

The Portuguese news agency Lusa reported from Luanda that a Spanish-built Casa 212 plane of Angola's TAAG airline crashed 20 miles west of Cuito, killing 25 people, including three Portuguese nationals. Lusa said the three were technicians with a Portuguese engineering firm in Luanda.

TAAG officials were investigating the cause of the crash, and no government official would comment on the rebels' claim of responsibility, Lusa reported.

The rebel statement claimed a Soviet-built Sukhoi 22 aircraft piloted by Cubans bombed a rebel base at Likwa on Wednesday in retaliation for the downing of the plane. That report could not be independently confirmed.

The U.S. military aid the rebels receive reportedly includes Stinger ground-to-air missiles. The guerrillas are said to have used the missiles in attacks on government supply and fighter planes in the past.

The French Foreign Ministry condemned the UNITA rebel movement for the kidnapping of Jean-Francois Grossenbacher and expressed regret that the rebels had been unable to fulfill a pledge to free him unconditionally.

Grossenbacher, 37, was captured Feb. 21 when guerrillas ambushed a convoy of Angola's state oil company. UNITA announced on Feb. 22 that it was willing to release Grossenbacher. The French statement said the technician died ''in the course of a prolonged march through very difficult terrain.''

Under a peace accord signed in December 1988, by Angola, Cuba and South Africa, Cuba withdrew 31,000 of its estimated 50,000 troops from Angola. Nevertheless, the fighting in the impoverished nation has continued.