Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

WASHINGTON — Interior Secretary Ryan Zinke is recommending that six of 27 national monuments under review by the Trump administration be reduced in size, with changes to several others proposed.

A leaked memo from Zinke to President Donald Trump recommends that two Utah monuments — Bears Ears and Grand Staircase Escalante — be reduced, along with Nevada's Gold Butte and Oregon's Cascade-Siskiyou.

Two marine monuments in the Pacific Ocean also would be reduced according to Zinke's memo, which has not been officially released. The Associated Press obtained a copy of the memo, which was first reported by The Wall Street Journal.

Trump ordered the review this year after complaining about improper "land grabs" by former presidents, including Barack Obama.

The Colorado River winds around the northern reaches of the Bear Ears National Monument, viewed from Dead Horse Point State Park near Moab, Utah. Jim Lo Scalzo / EPA file

Related: Trump Orders Review of Protected Federal Lands

National monument designations add protections for lands revered for their natural beauty and historical significance with the goal of preserving them for future generations. The restrictions aren't as stringent as those for national parks, but some policies include limits on mining, timber cutting and recreational activities such as riding off-road vehicles.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The monuments under review were designated by four presidents over the last two decades. Several are about the size of the state of Delaware, including Mojave Trails in California, Grand-Staircase Escalante in Utah and Bears Ears, which is on sacred tribal land.

No president has tried to eliminate a monument, but some have trimmed and redrawn boundaries 18 times, according to the National Park Service.

Zinke told The Associated Press last month that unspecified boundary adjustments for some monuments designated over the past four decades will be included in the recommendations submitted to Trump. None of the sites would revert to new ownership, he said, while public access for uses such as hunting, fishing or grazing would be maintained or restored.

He also spoke of protecting tribal interests and historical land grants, pointing to monuments in New Mexico, where Hispanic ranchers have opposed two monuments proclaimed by Obama.

Zinke declined to say whether portions of the monuments would be opened up to oil and gas drilling, mining, logging and other industries for which Trump has advocated. It was not clear from the memo how much energy development would be allowed on the sites recommended for changes, although the memo cites increased public access as a key goal.

A spokeswoman for Zinke referred questions Sunday night to the White House, which did not offer immediate comment.

If Trump adopts the recommendations, it would quiet some of the worst fears of his opponents, who warned that vast public lands and marine areas could be lost to states or private interests.

But significant reductions in the size of the monuments, especially those created by Obama, would mark the latest in a string of actions where Trump has sought to erode his Democratic predecessor's legacy.

Related: Obama Names Utah, Nevada Monuments Despite GOP Opposition

The recommendations cap an unprecedented four-month review based on Trump's claim that the century-old Antiquities Act had been misused by past presidents to create oversize monuments that hinder energy development, grazing and other uses.

The review raised alarm among conservationists who said protections could be lost for areas that are home to ancient cliff dwellings, towering sequoia trees, deep canyons and ocean habitats. They've vowed to file lawsuits if Trump attempts any changes that would reduce the size of monuments or rescind their designations.

Zinke had previously announced that no changes would be made at six national monuments — in Montana, Colorado, Idaho, California, Arizona and Washington.

In addition to shrinking six monuments, Zinke recommends changes at several other sites, including two national monuments in New Mexico: Organ Mountains-Desert Peaks and Rio Grande del Norte.

He also recommended changes to Katahdin Woods and Waters in Maine.