Saboteurs blew up a microwave communications station in Iran's southern oil-producing province of Khuzestan early yesterday in the most serious guerrilla action since oil and gas pipelines were ruptured by explosions two months ago.

The station's 300-foot-high steel communications antenna collapsed after it was hit by a rocket-propelled grenade, officials said, severing all outside communications with the oil industry center of Abadan and the port city of Khorramshahr.

The official Pars news agency blamed the sabotage on "counterrevolutionaries," but did not otherwise identify them.

Meanwhile, the National Iranian Oil Co. continued to operate without a chief executive following the refusal of Ayatollah Ruhollah Khomeini's Revolutionary Council to approve a Cabinet reshuffle announced by Prime Minister Mehdi Bazargan Friday.

Bazargan's choice for defense minister, Mostafa Ali Chamran, said the armed forces would be purged from top to bottom according to Islamic and revolutionary standards. Chamran added that Iran would continue to buy spare parts for U.S.-supplied military aircraft and helicopters, provided there were no political conditions.

In another development, U.S. charge d'affaires Bruce Laingen criticized the executions last week of three former Iranian senators in a meeting with the interior minister, Pars said.