The Reagan administration has "weakened institutions and processes that are important for the long-term operation of the [American] political system," including the budget process, the civil service and the White House, according to an Urban Institute study released yesterday.

The study, "The Reagan Presidency and the Governing of America," credits President Reagan with being a "popular president" who has successfully used the Oval Office to define the national agenda. But it said the administration's strategy has relied heavily on "the skills of individuals," including the president, and has lessened the effectiveness of the institutional system that governs the nation.

"The Reagan administration has demonstrated that with careful attention and a solid strategy, a popular president can make major inroads in defining the national agenda . . . ," the report said. "At the same time, the administration has made little attempt to institutionalize its approach and in some cases has actually weakened institutions, processes and centers of influence that are important to the long-run health of the political system and to the capacity of the presidency to perform its integrating function in American politics."

While applauding Reagan's first term as compared with a string of " 'failed' presidencies," the report said that "continued inattention to these processes and institutions for achieving consensus and building long-run governmental capacity would be costly indeed."

It said the administration's preference for personal lobbying, and use of the president to explain its priorities to the public and other politicians, has meant that the administration has "failed to forge a durable governing coalition that could extend its program, and often failed to recognize opportunities to build on existing support. As a result, it encountered stalemate on the budget and made little headway on its proposals for regulatory reform, private-sector initiatives and federalism reform."

The report says that Reagan's style of government -- in particular, having his political associates head the bureaucracy -- has hurt his efforts to effect change.

"Blind spots in the administration's outlook and approach led to significant missed opportunities," wrote the report's editors, Lester M. Salamon and Michael S. Lund, in an overview. "This was certainly the case in the regulatory arena where outspoken appointees effectively pulled the rug out from under the broad coalition that had formed in support of moderate regulatory reform, dooming many of the administration's regulatory objectives."

Similarly, on the budget, the administration was highly successful in its first year, the report said, but because of "inconsistent" support for the congressional budget process, the administration's record on budget matters for the rest of its first term was "mixed."