President Reagan, seeking to rally support for his defense buildup, will announce this week that he is implementing the Pentagon changes recommended in the Packard Commission report on defense management, administration officials said today.

The announcement is part of a continuing White House campaign to shore up sagging support in Congress for Reagan's defense budget, and comes as Congress is considering far-reaching legislation revamping the Defense Department.

The Senate is expected to take up legislation sponsored by Sens. Sam Nunn (D-Ga.) and Barry Goldwater (R-Ariz.) shortly after the congressional recess, aides said. It includes some provisions similar to those Reagan is endorsing this week.

The president is expected to seek congressional approval for some of the major changes outlined by the commission, which is chaired by industrialist David Packard, who was deputy defense secretary in the Nixon administration.

These changes include the creation of a new high-level Defense Department position to oversee weapons research, development and acquisition. The position would have the rank of undersecretary, and appears to have support on Capitol Hill.

Another revision sought by the Packard Commission, already in law, is a two-year cycle for military budgeting, scheduled to begin in 1988. Reagan is also expected to endorse the idea of a new post of vice chairman of the Joint Chiefs of Staff. This is already included in a House-passed bill and in the Senate proposals by Nunn and Goldwater.

It was also learned that Reagan has decided to implement unilaterally other recommendations of the commission, such as long-range defense budget planning, including five-year spending levels set by the president and the drafting of a military strategy by the Joint Chiefs to achieve goals within those limits.

Reagan appointed the 15-member panel last June amid reports of waste and fraud in Pentagon procurement programs, and as the White House struggled to prevent erosion in Reagan's $320 billion fiscal 1987 defense budget request.

In an "interim" report submitted to the president Feb. 28, the panel called for a major overhaul of the Pentagon's weapons acquisition system, citing structural problems "far costlier" than the well-publicized stories of exorbitantly priced coffee brewers and toilet seats.

The bipartisan commission concluded that "there is legitimate cause for dissatisfaction with the process" by which the Congress and Pentagon purchase weapons. The panel called for "major institutional change."

In accepting the document in a White House ceremony, Reagan promised to implement the recommendations "even if they run counter to the will of the entrenched bureaucracies and special interests."

A senior White House official said the purpose of this week's statement is to demonstrate that Reagan takes the Packard Commission report seriously and will make changes that could lead to military savings.

Also today, while the president continued his vacation at his ranch near here, senior aides met to discuss political and legislative strategy for the spring. The meeting was chaired by chief of staff Donald T. Regan and included political director Mitchell E. Daniels Jr., legislative liaison William Ball, Regan deputy Dennis Thomas, spokesman Larry Speakes, and other aides who spoke by telephone from Washington. A participant said the group reviewed long-range plans on such issues as taxes, budget and foreign policy but reached no major decisions.