Iran ordered four more atomic power stations from West Germany today in a multibillion-dollar deal that officials here called the largest unclear agreement ever signed.

A letter of intent signed by the Atomic Energy Organization of Iran and West Germany's Kraftwerk Union A.G. for the supply of four 1,2000-megawatt units - in addition to four already under construction - caught most observers by surprise. It indicated a new determination to meet an ambitious goal of installing some 20 reactors worth more than $28 billion by 1994 to provide domestic energy when Iran's oil starts running out. Contracts for two other atomic plants were concluded less than a month ago with France's Framatome after three years of haggling.

Officials indicated that Iran wanted a speedy agreement with Kraftwerk to take advantage of more favorable terms because of a lull in the West German atomic power industry due to anti-nuclear protests there.

The four plants are to be the same size as two the campany is now building at Bushehr on the Persian Gulf butlwill be located in arid central Iran and use a relatively new air-cooling technology to cut down on water consumption, said president of the Iranian Atomic Energy Organization. He declined to specify the cost of the power stations but others sources estimated that it could exceed $5 billion. The price of a West German-Brazilian package nuclear deal has been estimated at up to $6.8 billion but it consists of more than one agreement.

This latest Iranian deal raises to more than $11.5 billion the value of nuclear orders placed with French and West German firms since last year. Although Iran has expressed interest in buying up to eight plants from the Uinted States, American nuclear suppliers have had to watch from the sideliness as the deals eluded them because of the failure of the two governments to agree on a bilateral protocol that would goven nuclear exports to Iran.

The agreemnent has been held up by differences over the U.S. insistence on strict safeguards to prevent atomic weapons proliferation and Iran's demands for an assured nuclear fuel supply while maintaining sovereignty over its plants.

Last week a two-man U.S. State Department team visited Tehran to discuss the protocal, but no substantial progress was made, sources said.

Officials on both sides had hoped that a signficant agreement could be prepared for signing when the shah visits Washington next week to meet President Carter. Such a deal appears unlikely, the sources said. The Iranian side has been waiting to see nuclear export legislation now being debated in Congress.

Etemad said Iran would negotiate export credits from West Germany to financed up to 80 per cent of the cost of the four new plants, which are scheduled for completion in 1984 to 1987. The supply of equipment is firm under theletter of intent, but the financing construction and exact location of the units remain to be worked out.

Referring to the air-cooling system, Etemad told a news conference, "from now on all nuclear power plants in Iran will be based on this technology." He said it would be the first application of this technique on such a large scale.