WASHINGTON – Senator Edward J. Markey, who has faced criticism for wavering on how to respond to Syria, said Tuesday morning that he opposes the current Senate resolution to attack the country because “it is too broad, the effects of a strike are too unpredictable, and because I believe we must give diplomatic measures that could avoid military action a chance to work.”

Markey’s position has been the source of broad interest because he occupies Secretary of State John F. Kerry’s former Senate seat and because last week he was the only member of the Senate Foreign Relations Committee to vote “present” on a resolution to use force. The resolution passed on a 10-7 vote.

But the Massachusetts Democrat’s opposition to the current resolution may not matter now, as the Senate on Monday night postponed a vote to close debate on the authorization for force while the Obama administration pursues diplomatic options to removing alleged chemical weapons from the Syrian regime. Other lawmakers have been crafting alternative resolutions.

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“The use of chemical weapons is a heinous and horrific act outside the bounds of civilized conduct,” Markey said in a statement. “However, I am concerned about the unintended consequences of the strikes and the potential for triggering an even greater conflagration that could be beyond our ability to predict or control.

“After weighing all the information, I do not dispute the evidence that the administration has presented about Assad’s use of chemical weapons,” he continued. “However, I do not believe that the resolution as currently written is the most effective way for our country to accomplish its objectives in Syria. Moreover, I believe that such a military strike could actually make it more difficult for our nation to achieve its goals in this volatile region of the world.”

Markey’s decision not to support the measure could be embarrassing for Kerry, who for nearly three decades held the Senate seat that Markey now occupies. Kerry has been actively courting Markey’s vote, through a series of phone calls, and has been the Obama administration’s chief salesman to Congress.

Markey last week voted “present” when the issue came up in the Senate Committee on Foreign Relations. He said at the time he wanted more time to analyze the situation.

“My one concern is that we not get on a slippery slope — that we understand all of the steps that this action could lead to,” he told the Globe after the vote. “It’s about the resolution being too broad. It’s about the need for more information. It’s about my worry about a greater involvement in Syria.”

Asked why he did not just oppose the authorization, as did some of his colleagues who had similar concerns, he said, “A `no’ vote would have indicated I had sufficient information on which to base the decision. Which I did not.”