Edward Bennett Williams, the Washington Attorney, has been denied a visa to visit the Soviet Union where he hoped to help defend an imprisoned Soviet dissident.

Alexander Solzhenitsyn, the Soviet author and Nobel Prize winner now living in Vermont, retained Williams to defend Alexander Ginzburg, a close friend of Solzhenitsyn and his wife, who was arrested in February near his homme outside Moscow.

In an interview yesterday, Williams said the Soviet embassy here rejected his application for a visa and told him it would never be granted. Ambassador Anatoliy F. Dobrynin told Williams by telephone that his request for a visa was "unprecedented, presumptuous and arrogant," the lawyer said.

In an effort to help his client, Williams said, he will now take Ginzburg's case "to the court of public opinion." Publicity "is our last weaponry," Williams said.

The lawyer will testify Friday before the so-called Helsinki commission, an intergovernmental body created by Congress to monitor compliance with the European Security agreements signed inHelsinki.

He is also planning to solicit signatures of"leading Americans" on a letter to the heads of government of the states that signed the Helsinki accords to "point out the failure of the Soviet Union" to comply with their human rights provisions.

Williams said he would lobby with the U.S. government to "insist that the cases of lthe political dissidents (in the Soviet Union) be placed on the agenda" at the upcoming Belgrade conference of the Helsinki signatories. This conference is being held to assess the implementation of the Helsinki accords. It is scheduled to begin in June, though substantive discussions will not start until the fail.

Williams said he has had one telephone conversation with Ginzburg's wife in theSoviet Union, but that it was "jammed" after just two minutes of talk. Through other channels, the lawyer said,he has learned that Ginzburg has been held incommunicado since his arrest.

He has not been charged with a crime nor allowed to see a lawyer, Williams said.

Ginzburg, 40, was arrested on Feb. 4, shortly after he announced publicly that he had given away more than $360,000 provided by Solzhenitsyn to help the families of political prisoners in the Soviet Union. Ginzburg, a historian and a famous figure among the tiny band of dissidents in Moscow, served a previous prison sentence for making and distributing a transcript of the trial of two dissident writers in the mid-1960s

Williams yesterday released an open letter demanding Ginzburg's freedom signed by 326 Soviet citizens - an unusually large number of signatures.

Williams also said he had learned that Ginzburg has tuberculosis.He was arrested shortly after being released from a Soviet hospital where he was treated for pneumonia.

Williams said Solzhenitsyn and Mrs. Ginzburg both fear that Ginzburg may not be able to survive prolonged detention in the Kaluga prison outside Moscow. Williams said that prison does not have adequate medical facilities to care for Ginzburg.