Evidence allegedly implicating Michael V. Townley, convicted assassin of Chilean exile Orlando Letelier, in the 1974 slaying of a prominent retired Chilean general in Buenos Aires was submitted to a U.S. magistrate yesterday by the government of Argentina, which is seeking Townley's extradition.

After a hearing yesterday in Alexandria, U.S. Magistrate W. Harris Grimsley ordered Townley held without bond for an extradition hearing on July 22.

Documents submitted by the Argentine government, including several listing leads developed by U.S. prosecutors who investigated Letelier's death in a 1976 car bombing here, said a false passport used by Townley when Letelier was killed also showed Townley was in Argentina for several days before the Buenos Aires assassination and left the same day the general was slain.

That incident, also a car bombing, resulted in the deaths of Gen. Carlos Prats, an opponent of Chilean President Augusto Pinochet, and Prats' wife.

Townley pleaded guilty here to carrying out Letelier's murder on behalf of DINA, the Chilean security organization. He was arrested last month at Argentina's request on the same day he was due to be paroled from a federal prison after serving 62 months for the Letelier slaying.

Townley's lawyer, Jeffrey M. Johnson, argued yesterday that Argentina's "so-called proofs. . . barely meet the level of a mere suspicion" and accused U.S. prosecutors of a "behind-the-scenes betrayal" of a plea agreement under which Townley testified for the government in the Letelier case.

Assistant U.S. Attorney Leonie Brinkema said prosecutors will easily show a "definite, clear pattern of similarities" between the Letelier and Prats assassinations at next month's extradition hearing.