Defense Secretary Harold Brown, in the first trip of its kind, flies to China today for broad discussions on a range of issues, with the Soviet invasion of Afghanistan high on the agenda.

Pentagon spokesman Thomas B. Ross, outlining the agenda yesterday, said Afghanistan "undoubtedly will be a topic of dicussion" as Brown and his party survey the military landscape with their Chinese counterparts.

Other defense officials said that Brown will explore ways to build up the military capability of Pakistan on Afghanistan's border and extend help to guerrilla forces expected to combat the Soviet troops in Afghanistan.

The Chinese could contribute weapons to Pakistan, while Saudi Arabia has expressed an interest in assisting Afghanistan's guerrillas, according to administration sources. Both options will be explored in Peking.

Another topic is the offer to sell the People's Republic of China such American technology as a gound receiving station for the LANDSAT II satellite which whirls around the earth snapping pictures of crops, floods and forests. The satellite also carries sensors for detecting mineral deposits.

In internal discussions leading up to the decision to offer China the ground station, Carter administration leaders rejected the argument that China might use the information for military purposes. The United States would control what the Chinese received from the satellite, administration officials stressed yesterday.

Other topics of discussion include U.S. arms contol policy, specifically the strategic arms limitation treaty (SALT II) that President Carter asked the Senate to postpone yesterday and the agreement banning open-air tests of nuclear weapons. The administration, through these talks, hopes to nudge China toward agreeing to forgo further atmospheric tests of nuclear weapons.

Ross said yesterday that the Soviet invasion of Afghanistan and other developments in the Mideast and Indochina have not altered the administration's opposition to selling weapons to China.However, Ross reiterated the other part of the policy which states that the United States would not object to North Atlantic Treaty Organization countries selling modern weapons to China.

In a related development, the State Department announced yesterday that it had wrapped up an arms package for Taiwan. The package contains $280 million in Hawk and Chapparal anti-aircraft missiles as well as some anti-tank missiles. However, Taiwan's request for longer-range planes like quest for longer-range planes like the F4, F16, and F18 was rejected in the belief they would pose a threat to China.

Administration officials agonized over whether to announce the Taiwan arms deal before or after Brown went to China.One official said the decision to announce it before Brown's departure was dsigned to avoid the appearance that the talks in Peking influenced the makeup of the package.

Brown is the first secretary of defense to visit China while still in that office. James R. Schlesinger visited China after he had been fired from the post of secretary of defense by then President Ford.

Brown had been expected to fly home from Peking via Thailand but a new plan calls for him to return by way of Japan, where he will hold additional talks in Tokyo, and then stop in San Diego. Brown is expected to return to Washington on Jan. 13.

Pentagon officials involved with planning the China discussions emphasized that they would be largely exploratory over a wide range of topics and cautioned against expecting any conclusive agreements.

Any formal agreements most likely would come after further discussions subsequent to the upcoming meetings, officials said.