State Sen. A. Joseph Canada, the Republican nominee for lieutenant governor, yesterday challenged his Democratic opponent to speak out on an issue he said was a "most importan" one for Virginians: the Panama Canal treaties.

Although the treaties probably will be voted on in the Senate before or close to the time the next administration is inauguarated, Canada said he was opposing the canal because it was an issue that "I as a leader should speak out on."

Canada urged Virginians to "send a penny" to their senators to show opposition to the treaties. He asked of his opponent, Charles S. Robb, "Which side of the canal he is on?"

Canada, speaking at an Arlington press conference, called the treaties "dumb."

"Thousands of Americans died building that thing," Canada said.

A Robb spokesman replied to Canada's challenge by saying, "It's not a state issue, it's a national issue . . . as I understand it, lieutenant governor candidates are not being called upon to ratify it."

Canada cited Virginia Port Authority and Bureau of Mines figures to support his argument that the treaties would have a "real economic impact on Virginia."

The treaties, signed by President Carter last week, call for gradual return of the canal and the Canal Zone to Panama by the year 2000 but give the U.S. the right to defend the canal indefinitely. The U.S. is to pay Panama roughly $50 million a year until 1999, as well as other aid agreements and retains the right to keep whatever military base it deems necessary to the defense of the United States until then.

Echoing the objections of such anti-canal spokesmen as Ronald Reagan, Canada said "we paid for the land, we defended it, and now they want to give it away."

The first Panama Canal treaty, signed in 1908, was negotiated by the United States and a Frenchman who had headed a French company that was going bankrupt trying to build the canal. It gave the U.S. "all the the rights, powers andauthority which the United States would possess and exercise if it were the sovereign of the territory."

"When we have a Marxist government in the toll booth," Canada said, freight rates will rise and defense security will be in doubt.

"According to the Virginia Post Authority, of the $460 million Virginians realized in 1976 through the operation of their ports, $115 million was directly related to the use of the Panama Canal," Canada said.

He predicted the economic loss in Virginia would be in the "billions" if the treaties are ratified. He said a 9 per cent decline in the amount of coal shipped from Virginia's ports last year was due to Japan finding a source with cheaper freight rates, and predicted this type of decrease would continue if the canal rats go up.

Canada said the "Eastern liberal banking establishment" was pressuring the White House into supporting the canal because the Panamainian budget includes a large amount in interest payments owed to American banks.