Secretary of State George P. Shultz charged yesterday that "all of Central America" has become a target for subversion from Nicaragua, and expressed concern that the Soviet Union might use Nicaragua as a missile base.

Shultz defended U.S. policy in the region and criticized congressional cuts in military aid for El Salvador in a speech to the Chamber of Commerce and the World Affairs Council of Dallas.

Back in Washington, controversy continued over Reagan administration undercover support for Nicaraguan insurgents, a subject that was not discussed by Shultz in his speech. The Senate, according to several prominent lawmakers, is likely to be called into a secret session Monday by Sen. Christopher J. Dodd (D-Conn.) to discuss U.S. backing for the "secret war."

In the House, Rep. Tom Harkin (D-Iowa) said he has introduced a "resolution of inquiry," with 69 co-sponsors, requesting documents and details of U.S. support for paramilitary operation in Nicaragua. Under House rules, according to Harkin, the sponsors can obtain a vote on the resolution after 14 days if the information is not provided.

Shultz' speech, which was a full-scale public review of existing policy, centered on the strategic importance of the nearby Central American states, the dangers of "a new form of dictatorship" fostered by leftist states and the efforts of the United States to foster democracy and aid friendly nations in the area.

"Central America is so close that its troubles automatically spill over onto us, so close that the strategic posture of its countries affects ours, so close that its people's suffering brings pain to us as well," Shultz said.

Shultz said an old variety of dictatorship in the area, that of "economic oligarchy, political despotism and military repression," has been joined by a new variety, "that of command economy, a self-appointed elitist vanguard and guerrilla war."

Of this newer dictatorship, he charged, "Nicaragua has become its base, all of Central America its target."

As depicted by Shultz, the Sandinistas set out to restrict political, press and church opponents, to build "what is now the largest armed force in the history of Central America" and "to align themselves with the Soviet Union and Cuba in subverting their neighbors."

He went out of his way to refer to a recent comment by Nicaraguan Defense Minister Humberto Ortega "that Nicaragua would consider accepting Soviet missiles if asked." In the comment, part of an interview last Saturday with The New York Times, Ortega said that the Soviets had not proposed to place missiles there, but that "if they ask us we will examine the proposal and make our own decision."

Reps. Berkley W. Bedell (D-Iowa) and Robert G. Torricelli (D-N.J.), who were in Nicaragua last weekend, complained to Shultz in a letter Wednesday that administration discussion of possible Soviet missile deployments there "deliberately misled the American people."

The lawmakers said Sandinista leaders, identified by Torricelli as including Interior Minister Thomas Borge, had to be convinced to give a serious answer to questions on the subject because they considered it "patently absurd."

According to Bedell and Torricelli, Sandinista leaders finally said that missiles would not be accepted, even if offered by the Soviets, because Nicaragua signed and abides by the Treaty of Tlatelolco, banning the introduction of such weapons in Latin America, and because Soviet missiles would jeopardize Nicaragua's nonaligned status and the foundation of its revolution.

Shultz, in his Dallas address, said that "Nicaraguans in growing numbers have concluded that their struggle for democracy has been betrayed." He went on to say that the answer to Nicaragua's problems "is a political one" involving negotiations with neighboring countries and policy changes both internally and externally.

He made a strong appeal for congressional approval of additional military aid for El Salvador, charging that "in the middle of a war, the Congress has cut security assistance to a level two-thirds below the level of the previous fiscal year."

"Here you are fighting, and all of a sudden the flow of what you need to fight with is cut by two-thirds. Then people ask why the army is not doing better," Shultz said in a departure from his prepared text.

He evidently was referring to the fact that the administration was able to spend $81 million in military aid to El Salvador in fiscal 1982, including $26 million passed by Congress for that purpose and $55 million taken from a special executive branch emergency fund after the costly guerrilla raid on Ilopongo Air Base.

The failure to pass a worldwide foreign aid bill last fall left the administration with only a "continuing resolution" containing the same sum for military aid for El Salvador as was passed the previous year, $26 million.

Last month President Reagan asked for $110 million in additional military funds for El Salvador, $50 million to be provided by reallocating funds from other programs and $60 million to be included in a supplemental appropriation bill. Neither of those requests has cleared Congress, and both are in doubt.