Secretary of State Alexander M. Haig Jr. renewed his campaign against Cuban adventurism yesterday, warning that Cuba has "40,000 to 50,000 mercenaries deployed abroad" who are a "threat to peace and stability" around the world.

"The president is concerned and we are working actively on the problem," Haig said.

As in the past, Haig declined to say what action, if any, the United States may take against Cuba. But he added that Cuba's activities abroad have been "a focal point of our attention . . . since the outset of this administration."

Haig revived his anti-Cuban warnings during a question-and-answer session before the Freedoms Foundation in Valley Forge, Pa., where he was given the organization's American Patriot's Award. He acknowledged that his previous warnings about Cuban activity abroad have not always been well received at home.

"Sometimes our rhetoric is offensive to some elements in our country who do not like to hear calling a spade a spade," Haig said. But he added it would be wrong for officials to "condone excesses of the right or the left and fail to speak up courageously when these excesses occur."

Haig said the 40,000 to 50,000 Cuban mercenaries are deployed in Angola, Ethiopia, the Yemens and in Latin America.

"We Americans must view this as a serious problem and a threat to peace and stability," Haig said.

He said there are 3,000 Cubans in Nicaragua, in education and development, but also in military assistance.

Haig charged the Cubans are engaged in "subversion, propaganda and interventionism" in Colombia, Guatemala, Honduras and El Salvador.

Haig said the Cubans are "entrenched" in Angola six years after the United States had assurances they would leave. He added that Cuba has a "substantial force in Ethiopia, which is today in close alliance with South Yemen and Libya, in a pact which is dedicated . . . to overthrow the leadership of Saudi Arabia."

In the Mideast, Haig said he was "cautiously optimistic" that his talks Friday with Israeli Foreign Minister Yitzhak Shamir would lead to Israeli acceptance of European participation in a multinational Sinai peace-keeping force.

The Israeli Cabinet planned to meet today to discuss the compromise proposal that Haig discussed with Shamir. Before these talks, the Israelis had been expected to veto the participation of Britain, France, Italy and the Netherlands in the Sinai force because of statements that Israel views as contradictory to the Camp David accords.

But both Shamir and Haig emerged from their 7 1/2-hour meeting Friday voicing new optimism that Haig's compromise proposal could head off the Israeli veto.

According to an Israeli official, Haig proposed that the United States and Israel issue a new joint statement, declaring that the participation of the Europeans in the Sinai force would not detract from the Camp David accords and that the participation of the European nations did not mean their ideas would become part of the process.

Haig has viewed European participation as vital because it would mean for the first time that the Europeans had committed themselves to the Camp David process. But even if the Europeans are vetoed by Israel, Haig said, there will still be a Sinai force and the Sinai Peninsula will be returned to Egypt according to the provisions of the Camp David agreement.