Wielding his pen again, President Obama signed an executive order Tuesday to set aside public lands in California for a national monument, bypassing the Democratic-controlled Senate in the process.

Republicans blasted Mr. Obama’s move as another abuse of presidential power, while congressional Democrats hailed the action as necessary to surmount what they view as Republican obstruction.

In an Oval Office ceremony, Mr. Obama signed an order to protect more than 1,600 acres of coastline in California by adding it to the California Coastal National Monument. The president said he wanted to make sure the land “is going to be properly preserved.”

“I pledged to act wherever I could to make sure that our children, our grandchildren are going to be able to look upon this land of ours with the same wonder as we have,” Mr. Obama said.

The president also said the administration made sure to involve all stakeholders in the decision.

“Unanimously, in this part of the country, people believe that this is the right thing to do, and I certainly do,” Mr. Obama said.

The move was part of the president’s yearlong effort to emphasize actions he can take with his pen or his phone without the approval of Congress. But a top House Republican noted that it’s the Senate, not the House, that has failed to act on the land preservation issue.

House Natural Resources Committee Chairman Doc Hastings, Washington Republican, said Mr. Obama’s designation of the Point Arena-Stornetta Public Lands was unnecessary.

“Instead of using imperial powers, the president should pick up the phone and call upon Senate Democrats to take action,” Mr. Hastings said. “The House has already passed legislation, sponsored by a California Democrat, to expand the California Coastal National Monument by adding these lands. There is no inherent danger to this area or compelling reason for the President to take unilateral action now.”

Last July, the House passed legislation to add 1,255 acres from the Point Arena tract to the national monument. The Senate had yet to act on the House bill or its companion legislation, sponsored by Sen. Barbara Boxer, California Democrat.

Mrs. Boxer said she was “thrilled” by the president’s action and had urged him to take the step a year ago, contending that Senate Republicans were blocking her bill from consideration.

“It’s perfectly legal for him to do it,” Mrs. Boxer said. “We asked the president to do this by executive order because it’s stalled. Nothing was moving [in the Senate] in terms of lands bills. It was stalled by the Republicans [in the Senate], who said they didn’t want to do a lands bill.”

Western Republican lawmakers, and some Democrats, have expressed concern about Mr. Obama designating public lands unilaterally without input from local landowners, businesses and others. Congress hasn’t approved any new public-lands legislation since 2009.

Rep. Rob Bishop, Utah Republican, said Senate Democrats intentionally held up Mrs. Boxer’s bill, even after the House measure passed on a voice vote that signaled overwhelming bipartisan support, to give the president another opportunity to bypass Congress.

“The legislation was held up in the Senate, so the president could usurp the congressional process,” Mr. Bishop said in a statement. “In other words, the House was punked by the president. Had the Senate done its job, the bill would have been considered and passed under regular order. There was broad support for the measure.”