A federal judge in Alexandria yesterday dismissed a suit against the Export-Import Bank by a group of conservative Republican congressmen trying to block $96 million in loan credits and guarantees to Angola on the grounds that it is a communist country.

"I think it is a political question as to whether a country is a communist one and, as such, this court should not interfere with that," said U.S. District Judge James C. Cacheris. He also agreed with the government's contention that the plaintiffs lacked standing to bring the case.

The suit, which was filed in February, asked that the bank be stopped from disbursing any more funds under a 1984 loan package for a major offshore oil project involving Sonangol, Angola's government-owned oil company, and Cabinda Gulf Oil.

The suit put the Reagan administration in the ironic position of defending Ex-Im Bank loans to the Marxist Angolan government at the same time that it is sending weapons and other aid to Angolan rebel leader Jonas Savimbi in a CIA-run covert operation.

The plaintiffs, who included an Angolan political group opposed to the government there, contended that, under Ex-Im Bank rules written by Congress, it is illegal for the government agency to deal with communist governments.

Attorney Daniel C. Holdgreiwe, arguing for the plaintiffs, told Cacheris the issue was whether those rules prohibiting assisting communist countries were being violated. Holdgreiwe said U.S. credits permit the Angola government to free funds "to buy guns and bullets."

Justice Department lawyer Charles Sorenson said the bank is prohibited only from lending to 18 communist countries on a list drawn by Congress. Angola is not on that list. The plaintiffs were asking "the court to enforce their political point of view" on a foreign policy issue that is the responsibility of the secretary of State and the Congress, rather than the courts, Sorenson said.