Sen. Dick Clark (D-Iowa), after talks with President Carter and Secretary of State Cyrus R. Vance, last night urged "extreme caution" over any deeper U.S. military involvement in the conflict in Zaire.

Clark is chairman of the Senate Foreign Relations Subcommittee on Africa. Until last night he avoided any comment on the emergency airlift of about $2 million worth of American military and medical supplies to Zaire, to repel what it calls "an invasion" from across its border with Angola.

Military, diplomatic and intelligence information on the crisis in Zaire is "highly inadequate," Clark said, because "we have been almost entirely dependent on Zaire government sources."

"There may be justifiable grounds for assisting Zaire at this time," Clark said, "but this judgement cannot be made on the meager information available."

Clark said he has "no objection to humanitarian and nonmilitary assistance" being sent now to Zair, the former Belgain Congo, one of the largest nations in Africa.

"However," he cautioned, "I have serious doubts about the effectiveness of aid in this crisis, in light of the unstable situation in the country and the disorganization of the government's forces."

"I therefore urge extreme caution," Clark said, "until the facts of the situation are better known. Until the nature of the crisis is clarified, I do not think any deeper involvement is justified."

Clark said he sent a letter to Vance Thursday night, spoke to Vance by telephone yesterday, and then had a brief talk with President Carter yesterday morning, at the White House ceremony for signing the repeal of the Byrd amendment on Rhodesian chrome, which Clark led through the Senate.

Clark said that while he could not discuss what the President or Vance said, "they are very much aware of the caution that is needed in the situation."

"They are certainly not likely to be drawn into a military situation involving a civil war without very careful consideration," Clark said.

His reference to "a civil war" refers to the fact that the bulk of the troops which have crossed into Zaire from Angola are described as "Katanga gendarmes," returning to their home province of that name, which is now called Shaba Province. According to reports yesterday from Kinshasha, the capital of Zaire, the Katangan troops are being welcomed "with open arms" by many of their fellow-tribesmen in the region.

Vance said earlier in the week that the incursion could pose, "a dangerous situation" for Zaire and the rule of American-supported President Mobutu Sese Seko "if something happens to the copper mines" in the province under attack. The teetering economy of Zaire is based on copper mining. The attacking forces are now reported about 90 miles from the copper mining center of Kolwezi.

According to information available in Washington there are whites among the attacking force in Zaire. But Vance has said there is "no hard evidence" that they are Cubans.

The possibility that the Zaire conflict is linked to larger objectives of the Soviet Union and of Cuba in Africa is the greatest unknown factor for Carter administration strategists. The current U.S. estimate is that 14,000 Cuban troops still remain in Angola.

American intelligence assesments are reported to be pessimistic about the ability of Mobutu's army to cope with the current attack, even though the border-crossing forces are estimated by U.S. officials as 2,000 at most so far. Some U.S. estimates put the figure at 500 to 2,000.

Zaire's army is listed by the International Institute for Strategic Studies as 40,000 men plus 20,000 paramilitary forces. U.S. sources, however, claim that these figures are misleading, and that no regular Zaire government troops were in Shaba province when the fighting began on March 8.