A 17-year-old employe of the University of Maryland's golf course in College Park was struck by lightning yesterday and critically injured during one of the thunderstorms that punctuated Washington's third consecutive day of 90-degree temperatures.

The youth, identified as Loritz Clark, who works as a golf cart attendant, was near the course clubhouse in an area used for practice putting when the storm arose.

"It started looking real bad outside," said Ted Coon, a Maryland student who works as a starter at the course near Rte. 193 on the west side of the campus. "He was putting and he got struck." Coon said there was no rain, and the storm "came on real fast."

The thunderstorms, scattered and localized, cut off electricity to about 5,000 homes around the area yesterday, with Warrenton and Hyattsville being affected with particular severity, according to utility company officials.

Yesterday's high temperature, an ingredient of the atmospheric volatility that gave rise to the thunderstorms, was 90 degrees, recorded at National Airport at 12:45 p.m.

Today is expected to be about as hot, tomorrow and Wednesday perhaps a little less, but relief may arrive by Thursday in the form of a cold wave, said National Weather Service meteorologist Edwin Danaher.

The youth struck by lightning was taken first to Leland Memorial Hospital in Riverdale and then to the MedStar unit at the Washington Hospital Center. His address was not immediately available, but hospital authorities said he was a Maryland resident.

The incident was the third in May in Maryland involving death or injury as a result of lightning.

An inmate of the Maryland Correctional Training Center in Hagerstown died and two when they were struck May 18. On May 23, 13 people were injured, one of them fatally, in Baltimore when lightning struck the roof of the historic Leakin Park Chapel and flaming debris fell into the building.

When faced by lightning outdoors, people are advised to avoid open spaces, high ground, metal objects and isolated trees.