Dennis DeConcini - until a few weeks ago an obscure freshman senator - will meet this morning with President Carter, and the fate of the Panama Canal treaties could hinge on the outcome.

"DeConcini has got the entire Senate" where he wants it, a key Senate aide said last night, and many others shared the sentiment.

The Arizona Democrat's importance sarises from his sponsorship of a reservation to the treaty on the Panama Canal's future neturally approved by the Senate last month. The DeConcini reservation asserts a U.S. right to intervene in Panama unilaterally to keep the canal open.

Panama has strongly protested the reservation, and reports from Panama.

DeConcini will propose another reservation to the second canal treaty, and pro-treaty strategists regard that as the best availavble vehicle for some clarifying statement about intervention.

But this would need DeConcini's approval, and there was no indication yesterday of whether he would give it. Sources said one or two other senators would follow DeConcini'c lead on this matter, which could be enough to seal treaty's fate.

DeConcini said yesterday he would not be disturbed if the canal treaties were defeated because of his vote, if he felt he had to vote no on the second part. "I will take whatever responsibility people lay at my feet," he said, adding that he would be pleased to vote for the treaty if it includes the second reservation that he will offer. City have suggested that domestic political pressures might force Gen. Omar Torrijos, the country's leader, to reject the reservation.

Treaty supporters in the Senate and the Carter administration are now hoping that Torrijos and other Panamanians can be assuaged by some addition to the pending second treaty that will spell out America's continued commitment to the principle of non-intervention in other countries' affairs.

There appears no hope that the Senate would even consider revising or clarifying the actual DeConcini reservation. DeConcini said yesterday he saw no need for a change. He also said his reservation "does not give the United States the right to be involved in Panama's internal affairs unless the canal is closed."

In another development, Cheif Justice Warren E. Burger rejected a request from 60 members of the House for an injunction that would prevent President Carter from signing completed treaties until the Supreme Court decides on their lawsuit challenging the treaties' constitutionality.