WASHINGTON (AP) _ President Reagan, distracted by the Iran-Contra affair, ''seems dangerously disengaged from the business of governing,'' a Democratic House leader said Saturday.

''As we enter the president's final two years, the signals from the White House are not good,'' said House Majority Whip Tony Coelho, D-Calif., who delivered his party's weekly radio address.

''Most of his top staff is quitting and Mr. Reagan himself seems dangerously disengaged from the business of governing,'' he said.

''American cannot afford a passive presidency. We cannot succeed if the White House sleep walks through the next two years,'' Coelho said. ''Our competitors around the world, both economic and military, might try to take advantage. Republicans and Democrats want a strong presidency and the country needs one.''

Coelho urged Reagan to move quickly toward an arms control agreement with the Soviet Union and work with Congress to enact trade legislation.

''The Democrats in Congress pledge cooperation. We want the president to come off the sidelines and join us on the playing field. The issues are too important and the opportunities too great,'' he said.

''We don't have all the answers, but at least we're addressing the challenges that lie ahead,'' he said, referring to Congress. ''But the country can't be led by Congress alone.''

''The country has a lot of work to do in meeting the challenges it faces, but there's a sense the job isn't getting done. We want action and leadership, but there's some doubt about whether we'll get any from the Reagan administration in the next two years,'' he said.

He criticized Reagan's 1988 budget proposal for containing ''the same misplaced priorities'' that emphasize aid to the Nicaraguan Contra rebels and the ''Star Wars'' space-based missile-defense system.

''He wants more for Star Wars, but he's cutting the war on drugs. He wants more Contra aid, but not aid to education. He wants more Pentagon hardware, but not clean water,'' Coelho said.