The Reagan administration adopted a full-speed-ahead policy yesterday regarding cooperation with the Soviet Union, while reiterating its charge that the Soviet secret police has dusted U.S. diplomats with a "potentially harmful" chemical powder.

Agriculture Secretary John R. Block, in the most tangible expression of the administration's policy, was told to proceed as scheduled to Moscow tonight on a mission designed to promote Soviet purchases of U.S. farm commodities.

State Department spokesman Charles E. Redman said "there is absolutely no U.S. attempt in any way to sabotage prospects for the Geneva meeting" planned between President Reagan and Soviet leader Mikhail Gorbachev Nov. 19-20.

Redman said he made the statement in response to "those who would attempt to link the various events that have happened over the last few days into some sort of a long, drawn-out theory."

Other State Department officials denied any relationship among three events on the U.S.-Soviet front on the first three days of this week.

These were a tough speech Monday by presidential national security affairs adviser Robert C. McFarlane, the White House announcement Tuesday of an impending antisatellite test and the State Department announcement Wednesday of the "spy dust" charge.

"Each of these was on its own track" without administration planning or coordination, even about the timing, according to a senior State Department official.

"The timing of this whole issue was driven by the humanitarian health concerns for our personnel in Moscow," Redman said. He said the decision-making process regarding the "tracking powder" disclosures was "a relatively rapid one . . . over the past several weeks, once the nature of the problem became evident, and as a consequence our priority goal was to inform our employes."

A public announcement was synchronized with briefings in Moscow, Redman said, because "the story obviously was going to become public immediately" once about 200 U.S. diplomats and their families in the Soviet capital were informed.

"Rather than have that story be the subject of rumors and secondhand information, it was preferable, as soon as the embassy folks were briefed, to put the story out straight, so it could be understood," Redman said.

Under questioning from reporters, Redman gave no new details but declared that, "The evidence is there. We have absolutely no doubt in our mind that what we described as happening has been happening, in the manner in which we described it as happening."

Despite his characterization of the "dust" charge as "a serious issue," Redman expressed the hope that the Soviet side will not jeopardize "mutually beneficial bilateral cooperation" in such fields as agriculture, environmental protection and housing for diplomats.

Block's scheduled trip is "important to the overall political relationship" as well as potential export sales, the agriculture secretary said yesterday in Chicago.

Block said that sales of corn and wheat to the Soviet Union in the past 12 months were at an all-time high. An aide said Block will encourage the Soviets to buy even more, and that it would "probably not be appropriate" for the U.S. agriculture secretary to bring up the use of possibly harmful chemical dust against U.S. diplomats, their families and other Americans.

One U.S.-Soviet activity not going well is a volleyball match scheduled for today outside San Francisco. The State Department said three members of the Soviet consultate there were refused permission to attend because the arena is in an area closed to Soviet diplomats. The action also was in response to Soviet refusal three times in the past six weeks to approve closed-area travel by the U.S. consul in Leningrad, the department said.

Members of Congress, meanwhile, continued to call for reprisals because of the chemical dust.

Rep. James A. Courter (R-N.J.) asked President Reagan to order an end to the employment of Soviet citizens in U.S. diplomatic posts abroad within one year.

Courter said that the planting of chemical tracing agents by the KGB required "regular access" to U.S. diplomats, and that protection against such practices is "impossible" while more than 200 Soviet citizens are employed as service and maintenance personnel in U.S. posts in the Soviet Union.

Sen. Strom Thurmond (R-S.C.) said the United States should close its Moscow embassy "if necessary" to prevent Soviets from dusting Americans with chemicals.