The Reagan administration yesterday endorsed adoption of legislative-veto proposals, but only if the congressionally popular oversight tool applies to independent regulatory agencies and not to those in the Executive branch.

In testimony before a House Judiciary subcommittee, James C. Miller III, executive director of Reagan's regulatory task force, noted long-standing Justice Department questions about the constitutionality of the legislative veto, but said the administration could endorse some versions of the plan that apply to independent agencies.

An administration source, amplifying the statement, said the administration would oppose any so-called one-house vetoes, which would permit either the House or the Senate to block new federal regulations. The official stressed, however, that Reagan "would accept, perhaps even encourage," adoption of a limited legislative veto involving both houses and directed at independent regulatory agencies.

In his testimony, Miller said the administration "would be compelled to oppose any congressional veto provision that applied to Executive branch agencies."

Legislative vetoes are actions by one or both houses that would overturn a regulation or other agency action. One legislative-veto proposal before the House has more than 200 sponsors.

Miller's comments were made amid considerable confusion on Capitol Hill about the administration's views on regulatory reform. Reagan endorsed the legislative veto during the presidential campaign, and its adoption is a part of the Republican Party's 1980 platform.

In fact, Rep. Robert McClory (R-Ill.), ranking minority member of the Judiciary Committee, told Miller that he is becoming "a little concerned about the seeming confusion about regulatory reform." McClory said the administration's regulatory relief program -- which along with budget-cutting and tax-cutting are the major pieces of Reagan's economic package -- is behind the other two efforts.

Miller emphasized the importance of regulartory policy in the administration and said the omnibus regulatory-reform legislation before the Judiciary Committee and also before the Senate would receive "high priority" in the coming months.

The subcommittee is considering legislation that would revamp the regulatory process, setting out "major" rules for particular cost-benefit study.

Miller, who is also the Office of Management and Budget's administrator for information and regulatory affairs, said the administration is "troubled" by some sections of the complex legislation. Miller said the bill does not give the administration, and OMB in particular, enough power to determine when a new rule warrants detailed regulatory analysis of its potential costs and economic consequences.

"The president and his designees are clearly in the best position to exercise that control," Miller said. The administration would prefer legislation that would strengthen the power of the president to designate regulations for intensive Executive Branch oversight, Miller said.