The Senate Governmental Affairs Committee voted 13 to 1 yesterday to reauthorize the independent counsel act, but only after an outspoken Republican attack on the competence of two current special prosecutors.

Sen. Ted Stevens (R-Alaska) assailed independent counsel Lawrence E. Walsh as too old and rusty for the Iran-contra investigation, "someone who literally has passed his time." And Sen. Warren B. Rudman (R-N.H.) criticized independent counsel Whitney North Seymour Jr. for his "outrageous" attempts to subpoena the Canadian ambassador to testify at the trial of former White House deputy chief of staff Michael K. Deaver.

But Sens. Carl Levin (D-Mich.) and William S. Cohen (R-Maine) said they hope to bring the measure to the Senate floor before the August recess. They voiced confidence that the Reagan administration's contention that the law is unconstitutional will find little support.

The administration has warned, however, that President Reagan may veto the bill if it is passed in its present form, which would provide permanent authorization for special counsels.

Rudman offered, then withdrew an amendment that would have taken the power to appoint special counsels away from a special three-judge court and given it instead to the solicitor general in the Justice Department. Rudman vowed to refine his proposal and to carry the fight to the Senate floor. He also said he will offer a floor amendment to limit reauthorization to three or four years.

Rudman said the independent-counsel system has become an "old-boy network" relying on old resumes and dusty qualifications.

Rudman has been critical of the 75-year-old Walsh in the past but said he did not agree with Stevens. "I don't think Judge Walsh is over the hill," Rudman said.

Stevens said he was speaking as a former U.S. attorney "who served under Judge Walsh" in the 1950s when Walsh was deputy attorney general. The Alaska Republican voiced chagrin about Walsh on a number of points, from his occupancy of expensive downtown offices to his enlistment of Internal Revenue Service agents to see whether there are tax charges to be brought in the Iran-contra affair.

Walsh's prosecutors, meanwhile, appeared yesterday afternoon before Chief U.S. District Court Judge Aubrey E. Robinson Jr. to defend the legality of their appointments in the face of a court challenge brought by a lawyer for former White House aide Oliver L. North, a key figure in the Iran-contra inquiry. Robinson deferred ruling after arguments on whether Walsh's dual appointment in March by Attorney General Edwin Meese III makes it unnecessary to deal with Marine Lt. Col. North's claim that the independent counsel law is unconstitutional.