Shortly after Christmas, representatives of the rubber, food, auto and other industries crowded into the Pennsylvania Avenue conference room of ERT Inc. to prepare a shopping list of regulations they'd like the Reagan administration to scuttle.

About the same time, leaders of Washington's four chief business-lobbying organizations were writing to top officials in the Reagan transition team, spelling out a private proposal to bring regulatory agencies under tight control of the Office of Management and Budget.

As these and other initiatives demonstrate, the Reagan administration beckons like a stocked candy store to Washington's business lobby, which has battled for six years to contain and control hundreds of regulations on environmental, health, safety and consumer issues.

With high expectations, some business interests are reaching in with both hands, while others are apparently hanging back or looking to Congress as the most important source of help, at least in the short run.

Eric O. Stork, the official of the ERT consulting firm who assembled the industrial representatives, handed them a questionnaire that asked for details of their regulatory problems with the federal government. Their answers -- which Stork declines to discuss -- were assembled at the request of OMB Director David A. Stockman, a mainspring in the Reagan administration movement to get government "off the back" of business.

The Jan. 8 letter from the four business organizations -- the Business Council, Chamber of Commerce, National Association of Manufacturers and National Federation of Independent Business -- made proposals that would provide a powerful legal basis for companies to attack government regulations as too costly or unreasonable, and would create a five-year review period to determine the fate of all major regulations.

The letter also reminded the Reagan aides that "an opportunity for decisive actions exists now as never before."

The reminder was probably unnecessary: there is no question about the sentiments of President Reagan and his top aides on deregulating business. In his economic address Thrusday, the president charged that excessive regulation has stifled the growth of business while adding $100 billion a year to consumer costs.

Easing regulatory requirements on business is a central part of Reagan's economic plan. Stockman and other key administration officials have long supported the policy changes called for by the Business Council and the other authors of the Jan. 8 letter, particularly the demands that federal agencies choose the least costly approach and then only when the benefits of regulation are reasonably related to the expense.

OMB, under Stockman, is becoming exactly the regulatory monitor that the business groups were asking for, preparing presidential orders to see that Reagan's philosophy is followed by federal bureaucrats.

However, the appearance of a onesided friendship with business is not something the Reagan administration wants.

Robet K. Gray, vice chairman of Hill & Knowlton Inc., a lobbying-public affairs firm with close ties to the new administration, says some of his clients expect the Environmental Protection Agency and the Occupational Safety and Health Administration to be gutted."Some businessmen think that's on tomorrow's agenda. It won't be," Gray predicted.

The president "is not going to be able to be politically reckless . . . The new administration can't afford to be 'for' cancer or pollution," said Gray, and a frontal attack on principal OSHA or Epa regulations could implant that impression on the public. Industry will have to prove its case for deregulation, he said.

John Post, Washington representative of the Business Council, minimized the significance of the January letter. "We don't expect a response. A shift in regulation would have occurred regardless of the outcome of the presidential election," he contended. "The time is ripe."