The number of Virginians laid off because of the energy shortage and severe cold weather has officially reached 10,500, the Virginia Employment Commission reported yesterday.

Since the total is based on those workers who have filed for unemployment benefits, the actual number could be higher. Thousands of others are working shorter weeks.

The layoffs, the commission said, are a result of frigid weather that has iced out watermen and construction workers, gas curtailments that have idled factories and the statewide energy emergency that has reduced businesses to a 40-hour week under a gubernatorial order.

While the weather showed a slight improvement yesterday - the high at National Airport was 38 degrees and the low was 22 - Washington Gas Light Co. said it was extending its natural gas curtailment to "nonessential" customers from Saturday to 8 a.m. Wednesday. Baltimore Gas and Electric Co. also extended its curtailment to the same time.

Both utilities took the action, they said, because their supplier, Columbia Gas Transmission Corp., has been unable to build up its depleted supplies because of continuing cold in the Middle West.

Washington Gas Light spokeswoman Sheryl Rutledge said that on Monday - the first full business day of the curtailment - there was a 10.8 per cent reduction in gas consumption in the metropolitan area compared to what the gas consumers would have been expected to use without conservation measures. A 10 per cent reduction was reported by Baltimore Gas.

The curtailment has affected all commercial and industrial customers not supplying "essential" services. Residents have not been affected.

In Virginia, state energy officials were unable to estimate the energy savings from Gov. Mills E. Godwin's order of last Saturday limiting most businesses to 40 hours weekly until Feb. 13.

However, a spokesman for a metropolitan food chain said "we expect to have very minor savings" because of the reduced hours of operation.

The spokesman, who declined to be identified, said food industry officials hope to arrange a meeting with the governor by the end of the week.

In Maryland, Gov. Marvin Mandel asked the attorney general's office to prosecute violators of his emergency order, less drastic than Godwin's. Under Mandel's order, stores and other businesses cannot use lighting for "decorative or advertising purposes," and must eliminate nonessential illumination in parking lots.

The Maryland curtailment of natural gas was extended to some light industries in the western part of the state, a move that state officials said would lead to more layoffs.

The Virginia Employment Commission reported that 2,097 workers laid off by the energy crisis filed for unemployment benefits yesterday, a figure down from the 2,920 applications filed on Monday.

The VEC has no figures on the number of employees working reduced weeks because many of them are not eligible for benefits.

VEC officials said most of the energy-related layoffs have occurred east of Richmond and in other industrial areas of the state to the south and west. Relatively few of them, they said have occurred in Northern Virginia, which has only 12,000 industrial employees in a work force of more than 40,000.

However, Giant Food is not using the 585 part-time workers who normally help staff its 39 stores in Northern Virginia, which are open only 40 hours weekly during the energy emergency.

In another development yesterday, the Maryland Public Service Commission announced that a new rate structure will go into effect this week in Montgomery and Prince George's Counties.

The change is a result of the commission's modification of a recent rate change by Washington Gas Light Co.

According to Public Service Commissioner Michael D. Barnes, the change will mean an 8.63 per cent increase in revenues for the utility and will lower gas bills for small gas users, while raising them for customers who use more than the average amount of gas.

At Ladysmith High School in Caroline County near Richmond, 15 students were arrested after 60 pupils refused to go to their 50-degree classrooms because they were too cold.

The arrests came after the students moved into the hallways in a 45-minute protest that began about 9 a.m. Authorities had told the students to be patient until the temperature was raised.

Under Gov. Godwin's emergency oorder, schools have been told to keep their classrooms at 65 degrees. But the Ladysmith High School heating system somehow was turned off altogether Tuesday.