Secretary of Transportation Brock Adams yesterday ordered new early deadlines for the installation of safety devices on rail tank cars that carry hazardous materials.

More than 20,000 of the jumbo tank cars, which usually carry material such as anhydrous ammonia and liquified flammable gas will be affected by the order, which will go into effect July 12, after a period for public comment.

The timeable calls for shortening the time previously allocated to the owners of the cars to install several protective devices. The action was facilitated by a rash of rail accidents - some fatal - involving cars carrying hazardous materials.

Adams set the following new deadlines:

New safety couplers must be installed on all of the 20,000 cars by Dec. 31. (The original deadline was July 1, 1979.)

Protective head shields must be put on about 7,500 cars, and full-jacketed insulation on another 7,900 cars by Dec. 31, 1979 (original deadline; Dec. 31, 1981).

Thermal coating must be applied to all tank cars carrying flammable gas that are scheduled for "spray on" treatment, and jacketed insulation and head protection on the rest of the cars by Dec. 31, 1980. (original deadline: Dec. 31, 1981).

"The revised schedule I am proposing today represents our best judgment on the extent to which the work can be accelerated while still achieving the long-term value of the full jacketing system, which three of the four major tank car companies plan to use," Adams said in his speech to the Manufacturing Chemists Association luncheon here.

"The public has a right to be worried," Adams said. "About 4 billion tons of hazardous materials are shipped each year in the U.S. That's nearly double the amount shipped 10 years ago."

Adams said that DOT will be - and has been - taking several actions aimed at putting more bite into safety regulations.

"Fines for safety violations were up 126 percent in 1977 over 1976," he said, predicting that collections this year would run even higher.

"We are also cracking down on hazardous materials violations. These were once treated as criminal cases, and in the busy criminal court system had a low priority," he said.

He also said he is asking for a "40 percent increase in the number of FRA track inspectors."

A railroad tank car industry spokesman said that the industry was "anxious to comply" with the new timetable.

Robert Smith, president of the Railway Progress Institute, said, "We are pleased that the Department of Transportation has moved quickly on this matter and are anxious to comply with the most workable final rule that ultimately emerges."

And a statement from the Association of American Railroads also indicated that the cost of retrofitting all of the cars involved in the announcement is about $10,000 a car. "The cost is being borne by the owners and lessors of the giant tank cars," the statement said.

Railroads themselves own only a few of the highly specialized cars, which average only eight trips a year and spend most of their time on private sidings as storage units for customers ranging from utility companies to farmers, the AAR said.