President Reagan will ask Congress for $270 million in new military aid for Nicaragua's contras "at the appropriate moment" between the Nov. 7 deadline for implementing the five-nation Central American peace plan and Nov. 30, Secretary of State George P. Shultz said yesterday.

Shultz announced this timetable during a speech in Chicago, where he continued the administration's campaign, launched Tuesday by Reagan, to persuade the public and Congress that continued contra aid is needed to ensure that Nicaragua's Marxist government complies with the peace agreement signed in Guatemala last Aug. 7.

"Continued aid to the freedom fighters is key to the full implementation of the Guatemala agreement," Shultz said. "The reality of our assistance to the resistance is what made the agreement possible. Its continued availability is just as essential to ensure that the Guatemala agreement is implemented in a way that secures a negotiated cease-fire and a democratic opening in Nicaragua."

U.S. funding for contra military activities expired Sept. 30. And Shultz told Congress last month that the administration wants the $270 million to sustain the contras for the next 18 months. However, revelations in the Iran-contra hearings about diversion of profits from the sale of arms to Iran to the contra effort rekindled congressional opposition to contra aid and caused the administration to delay its request in the hope that congressional hostility would diminish.

House Speaker Jim Wright (D-Tex.), who joined Reagan in a bipartisan peace proposal for Central America during the summer, has urged the White House to heed the pleas of Central American leaders including Costa Rican President Oscar Arias, principal author of the Guatemala plan, and hold back any contra aid request until after Nov. 7. Wright also has warned that Congress would reject the request if it is made before the possibilities of the peace agreement are exhausted.

Reagan began a new effort to win backing for contra funding with a speech Wednesday to the Organization of American States that administration officials said was intended to be conciliatory. However, while Reagan repeated assertions that he welcomed the Arias plan, he said it failed to address U.S. concerns about Nicaragua's ties to Cuba and the Soviet Union, and he sharply criticized Nicaragua's Sandinista leaders as totalitarian dictators who are determined not to permit true democratization of their country.

Shultz, in his speech yesterday, sounded the same themes. Reiterating U.S. demands that the Sandinistas negotiate with the contras on a cease-fire and stop receiving Cuban and Soviet military aid, Shultz said:

"We cannot place our strategic interests at risk in the mere hope that positive internal change will take place in Nicaragua. It is our responsibility to make certain that the Wright-Reagan peace plan and the Guatemala agreement are implemented and that there be no Soviet or Cuban military presence in Nicaragua and that Nicaragua pose no military or subversive threat to its neighbors or the region."

He said the United States, to further its interests, is maintaining close contact with the democratically elected leaders of the other four countries in the peace process, Costa Rica, El Salvador, Guatemala and Honduras. He added: "And when the right point is reached, you will be seeing me in Central America, too."