The Office of Management and Budget said yesterday it will block the Environmental Protection Agency's package of proposed changes in the standard for lead in gasoline until the agency revises it.

EPA sources said they fear that OMB is trying to force relaxations in the strict standard the agency wants.

At the urging of industry, the Presidential Task Force on Regulatory Relief last year asked EPA to relax the standard. But the resulting public outcry prompted EPA to oppose OMB and tell reporters that it would come out with a standard that, in many respects, is considered stronger than the existing one.

OMB, under a Reagan administration executive order, must approve all regulations before they are published in the Federal Register.

At present, the average amount of lead added to gasoline by large refiners must not exceed 0.5 grams per gallon of all the gasoline (leaded and unleaded) they produce. The limit for small refiners ranges from 0.8 to 2.65, depending on the size of the operation, but that waiver is scheduled to expire on Oct. 1.

EPA's new proposal would regulate lead in leaded gasoline only, and is expected to reduce airborne lead by an additional 31 percent over the next eight years. Large refiners would be subject to a limit of 1.1 gram per gallon and small refiners would be limited to 2.5 grams.

The EPA proposal would also tighten the definition of small refineries, reducing the number of firms that are eligible for the exemption from 159 to 74. The agency wants then to issue an interim final rule that would require most of the firms that lose their exemption to meet by Oct. 1 either the old 0.5-gram standard for all gasoline or the 1.1-gram standard for leaded gasoline.

This final rule is aimed at the so-called blenders, who add large quantities of lead to inexpensive gasoline components. These firms have sprung up in recent years because of the special exemption for small refiners. EPA sources said the rule would decrease airborne lead by about 5 percent, or about 3,000 tons of lead over the next year.

In a letter to EPA associate administrator Joseph A. Cannon, Christopher C. DeMuth, administrator of OMB for information and regulatory affairs, said he was "troubled by some aspects" of EPA's proposal, which "needs to be rectified before the rule is issued."

DeMuth specifically opposed the interim final rule, saying that all small refineries should be allowed to meet the easier standard until a final proposal is adopted.

In addition, DeMuth wrote that EPA should, during the rest of the rulemaking, "focus" attention on the "appropriateness" of the 1.1-gram standard.

In private conversations with EPA officials, OMB has noted that, as more cars on the road require unleaded gasoline, lead levels in the air will drop. OMB originally asked EPA to allow the gasoline lead level to rise every year so that the total lead in air would remain about the same, according to OMB and EPA sources. EPA refused.

EPA sources said OMB is now trying to have them raise the limit to 1.2 or 1.3 grams. EPA staff said the 1.1-gram standard was chosen because it would allow roughly the same amount of airborne lead as the existing standard.