A British cargo plane flew emergency supplies from Bangkok to the Cambodian capital Phnom Penh today, and it was announced that the Cambodian government had given approval to a 30-nation effort to head off massive starvation in that war-torn country.

The flight by the Hercules turboprop, loaned to the International Red Cross and UNICEF by the British Royal Air Force, marked the start of what relief officials hope will be a regular daily shuttle of supplies. The plane returned to Bangkok after unloading its cargo of vehicles to help in the distribution of food and medical aid.

The relief agencies plan to start two round-trip supply shuttles each day, beginning Sunday. There had been some doubt that the Phnom Penh government of Heng Samrin would grant permission for the daily flights since part of the relief is scheduled to go to rival Pol Pots forces. But approval was announced today by a UNICEF spokesman.

In Geneva, the Red Cross said Friday it was starting the main phase of its $110 million six-month relief program for the Cambodian population, which is said to have dipped from 7 million to 4 million during the social upheaval and civil war since the communists took power in 1975.

In Washington, the State Department announced it was ready to send $7 million in rice and other food to Cambodia after resolving legal questions on delivering the aid.