FRESNO, Calif. (AP) — Weary crews battling wildfires across northern and central California are going to get help from the National Guard, the first time the military has been called to ground-based firefighting duty since 1977.

Gov. Arnold Schwarzenegger on Tuesday ordered 200 guardsmen to report for fire training to begin assisting on the fire lines early next week. The extra hands are expected to boost the nearly 19,000 personnel currently fighting the fires.

“I think that they all are doing a great job, but the danger is that our firefighters get stretched thin,” the governor said. “A lot of them are working overtime, and they are staying up there for more than 12 hours, sometimes 24 hours, 36 hours. So we have to be very careful that they get enough sleep and they get enough rest.”

The governor and the head of the Federal Emergency Management Agency, David Paulison, planned to visit Big Sur on Wednesday for a briefing on firefighting efforts in that hard-hit region.

Already this year, drought conditions, high temperatures and a series of lightning storms have contributed to more than 680 square miles of land being charred statewide.

Federal fire managers predict an increase in severe wildfire activity in northern California through October due to unusually hot, dry weather and scant rain.

The National Interagency Fire Center, headquartered in Boise, Idaho, issued a 2008 Wildland Fire Outlook on Tuesday forecasting significant fire activity to increase or persist in California, as well as in parts of the western Great Basin in Nevada, the northern Rocky Mountains, Texas, and West Virginia.

The agency also upped its national preparedness level Tuesday to Level 5, its highest — a warning that there are major fires that have the potential to exhaust firefighting resources. It’s the second earliest date the agency has reached Level 5 since 1990.

California has endured the worst of the fires so far this year, raging from the western edge of the Sierra Nevada to coastal mountains near Big Sur. They have created a smoky haze so stifling that some doctors in the San Joaquin Valley say their waiting rooms have been crowding with patients struggling to breathe.

In the Big Sur region of the Los Padres National Forest, about 200 people along a roughly 15-mile stretch of Highway 1 were ordered to leave their homes and businesses. Evacuation orders also remained in place for occupants of at least 75 homes who were forced to leave the region last week, as a 47,000-acre blaze burning through uninhabited forest land moved closer.

In Southern California, a fire in the southern extension of the Los Padres forest north of Santa Barbara also prompted mandatory evacuations as wind up to 35 mph pushed flames toward homes in the foothills of the Santa Ynez Mountains. Officials said the fire had burned nearly 100 acres of heavy brush by Wednesday morning.

Santa Barbara County Fire Capt. Eli Iskow said about 40 homes were evacuated. County spokesman William Boyer said he didn’t know how close flames had gotten to homes.

In the Sequoia National Forest east of Bakersfield, crews struggled to contain an 11,500-acre blaze there. Powerful gusts and choking smoke traveling up the steep canyons hampered their progress, and residents of neighboring towns were ordered to evacuate.

Even without the blazes, the farming towns and subdivisions dotting the valley are typically shrouded in a layer of smog during the summer. But airborne ash from the blazes caused such a spike in air pollution over the weekend that meteorologist Shawn Ferreria said it took his breath away.

“I went and bought a mask because my lungs were not happy with me,” said Ferreria, a senior air quality specialist for the San Joaquin Valley Air Pollution Control District. “What we are experiencing is out of historical norms.”

Officials had hoped a fog bank along the Northern California coast would help with fire suppression, but the moisture did not extend inland, said Brian Tentinger, a meteorologist with the National Weather Service in Monterey.

Air district officials grew concerned that wind patterns could send more smoke billowing into the valley, which is bordered on three sides by mountains. Once the tiny particles of soot — which are blamed for triggering asthma and other respiratory problems — are carried inland, they’re sealed in under a layer of warm air created by hot summer temperatures.

“Our waiting rooms are full of people with sore throats, itchy eyes and sniffles,” said Kevin Hamilton, a respiratory therapist with Sequoia Community Health Center in Fresno.

Schools canceled outdoor activities and residents were warned to stay inside with the air conditioner running. For households lacking air conditioners, the district recommended families hole up in local malls.

“Since there’s fires to the north, west and east of us we’re kind of surrounded,” said Gary Arcemont, a meteorologist with the Fresno-based air district. “Depending on what happens with the intensity and the winds in the next few days, we could be breathing the smoke from any of them.”