Another day of 100-degree heat scorched the eastern half of the country, combining with the drought to force water conservation by millions of people, and Chicago issued a "yellow alert" to warn against its worst smog in a decade.

A Pennsylvania infant, whose mother apparently forgot about her, died in the back seat of a car where she was left for five hours in 100-degree heat, and water restrictions imposed on Columbus, Ohio, residents, have created a new city force of water police.There was no relief in sight from the weeklong heat wave that has shattered temperature records that stood for more than a century. Rec-ord highs were reached Thursday in 36 cities in 10 states from the Midwest to the Middle Atlantic coast.

During a heavy thunderstorm Thursday in Brownsville, Texas, a department store collapsed, killing at least 11 people and injuring 42, authorities said. Workers rescued a woman and a 2-year-old girl from the rubble Friday. (Story on A1)

More than 4 inches of rain fell in Odessa, Texas early Friday. Water 2 feet deep was reported in an intersection in Midland, Texas, stalling numerous cars and flooding overpasses.

In Lea County, N.M., flooding was reported inside 40 homes and 10 businesses.

Thunderstorms also rumbled over parts of the Rocky Mountains and the Great Plains Thursday. But meteorologists say several days of drenching rain are needed to ease what they describe as the most devastating drought in a half century.

Columbus, Ohio, officials received about 300 calls from residents reporting their neighbors were violating a lawn sprinkling ban imposed Thursday.

"We had 104 calls in the first hour," said Jackie England, a Division of Water official. "I'm not surprised that people tried to squeeze in one last sprinkle. What surprises me more than anything is that so many people took the time to call in violations."

Repeat offenders face a jail term and a $100 fine.

This week's heat only adds to the woes of the blistered Farm Belt during the critical "tasseling stage" for corn when the plant requires more moisture to reproduce.

"The drought is worsening and we're facing imminent disaster," Illinois Agriculture Director Larry Werries declared.

In Washington, the governors of seven Midwestern states won assurances from Congressional leaders Thursday that drought-relief bills will be filed early next week in an attempt to send legislation to President Reagan by mid-August.

"The dimensions of this drought are astronomical and very far-reaching," North Dakota Gov. George Sinner said. "Our wheat crop is about two-thirds gone. It's just not there. We can't afford to lose any more of our farmers. With them go farm community businesses."

The drought now has damaged crops in 1,880 counties in 37 states from California to Vermont and drained the nation's rivers to historic lows. Wildfires have blackened 401,700 acres in the tinder-dry West and Alaska, and at least 179 firefighters have been injured.

The state of Pennsylvania joined Cleveland, Minneapolis, Baltimore and suburban Detroit in taking steps to conserve water Thursday. Baltimore and two nearby counties banned all outside water use, warning violators that their water could be turned off. Lawn sprinkling was banned in Minneapolis, in 11 Detroit suburbs and in Cleveland and 70 surrounding communities.

Pennsylvania asked residents to voluntarily cut water use 5 percent.