The U.S. Weather Service issued a "heavy snow warning" yesterday for the Washington area today as one winter storm swept up out of the Southwest and a second battered the Rocky Mountains, Great Plains and the Midwest.

With 4 to 8 inches of new snow predicted for last night and today, and a mixture of snow, sleet, freezing rain and rain expected by tonight, weather service meteorologist Jerry LaRue said last night that today's morning and evening rush hours would "be quite bad" if the storm develops as forecast.

As of late yesterday, LaRue and his fellow forecasters warned that the forefront of the snowfall might begin falling intermittently before midnight.

"But then," said LaRue, "we expect heavy snow, giving us the 4 to 8 inches over the metropolitan area.

"The heavy snow will be over by tomorrow (Tuesday) evening," he said, "gradually changing to a mixture of snow, sleet, freezing rain and rain. We'll have periods of that type of thing continuing through Wednesday."

Temperatures are expected to remain below the freezing point through this morning, with overnight lows predicted in the upper 20s in the city to about 25 at Dulles International Airport.

The storm is part of the front that moved out of Texas, bringing slightly warmer temperatures -- as well as snow -- with it.

At the same time, another separate storm is making life miserable all the way from Colorado to Illinois and Indiana.

Fifteen inches of snow blanketed Durango, Colo.; the Missouri legislature canceled its session because of snow in that state and authorities in some areas of Kansas, Oklahoma and Arkansas were urging persons not to travel on snow and ice-covered roads.

Several traffic deaths were attributed to the storm in the Midwest, and temperatures dropped to as low as 30 below zero in North Dakota.

The snow and ice that still coated some roads in this area from last week's storm thwarted newsmen tracking former President Nixon yesterday as he drove to Dulles Airport to catch a plane for California.

More than a dozen reporters were staking out Byrnely Farms, an estate near The Plains, Va., where the former President stayed while in the area to attend memorial services for Sen. Hubert H. Humphrey.

Four cars of television network camera crews and reporters slid off the steep entrance road to the estate and two trucks had to be called to pull three of the cars from a snow bank and one from a creek.

Nixon, meanwhile, was driven without incident by the Secret Service to Dulles where he caught his 11:45 a.m. flight to Los Angeles.

Elsewhere in the metropolitan area, life was basically back to normal following the five-inch snow storm last week, but many side streets and back roads remained ice- and snow-covered.

Weather service officials said yesterday that if the storm predicted for today lives up to its billing and dumps eight new inches of snow, we could be well on our way to having an above average snowfall this winter.

Such a fall would give the area a total of 13 inches, with January only half over and the normally heavy snow month of February still to come. The average annual snowfall for the Washington area is 17 inches, according to the weather service.