A political power struggle over the convention chairmanship has blocked the opening of the World Administrative Radio Conference in Geneva for the third straight day.

Despite three meetings yesterday of the chairmen of the 146 national delegations attending the conference, no agreement was reached on a consensus candidate for chairman to be presented to the full convention for ratification.

The conference convenes every 20 years to allocate world radio frequencies and to prevent interference between countries using the spectrum.

Since their inception in 1865, the conferences have been highly technical. Under the supervision of the International Telecommunications Union, they have been largely dominated by the United States and the other industrialized nations.

But prior to this year's conference, nonaligned and developing countries began a campaign for a "new World Information Order" that would dramatically redefine the nature of telecommunications and end the dominance of the airwaves by the developed nations.

At their recent meeting in Cuba, the nonaligned nations passed a resolution calling on all members to support the election of a conference chairman who comes from nonaligned ranks.

In three days of closed-door sessions since the 10-week convention was scheduled to start Monday, however, the delegation chairmen have not been able to agree on a chairman. Candidates from India, New Zealand, Algeria, Argentina and Mexico have so far failed to attract a consensus.

The one-country-one-vote convention could still elect a chairman by balloting, but U.S. officials fear that a decision to ballot rather than follow the traditional vote by acclamation could set a dangerous precedent.

Because agreement on broadcast spectrum usage requires the cooperation of all nations, voting on technical issues is generally by acclamation. If that were to change, it would raise the possibility that those who did not vote for a certain restriction would not abide by it, U.S. delegation sources said.

"All we want is to accept a consensus candidate as soon as possible and get on with the technical aspects of the convention," said State Dept. official Wilson Dizard, deputy chairman of the 65-member U.S. delegation, in a telephone interview from Geneva.

The delay of the conference opening is the first such postponement in the history of the telecommunications union, which is the oldest specialized agency operating under the United Nations.

If the convention remains politicized, the impact on world telecommunications could be dramatic.

If, for example, the United States decided to go ahead on its own with a plan to divide the present UHF band, and give up television slots to land-mobile uses, Canadian UHF stations near the border would probably experience interference from landmobile users.