Sudan and Egypt went to considerable lengths today to play down reports from Washington about a Libyan-backed plan to topple the government of Sudanese President Jaafar Nimeri.

Reports reaching here from the Sudanese capital, Khartoum, quoted official government sources as saying there had been no coup attempt and that only 25 persons had been arrested during the past three months for antigovernment activities.

The unidentified sources said weapons and explosives had been found among those arrested and that they had been trained in Libya to carry out "subversive acts against the Sudan." The sources also said that those apprehended belonged to "revolutionary committees" involving various opposition elements.

Egyptian officials also minimized the Libyan danger to the Nimeri government. Emerging from a meeting with U.S. Assistant Secretary of Defense Francis West, Egyptian Defense Minister Abdul Halim Abu Ghazala told reporters he did not see "any signs of a crisis or a possible aggression on Sudan at present."

Egypt has shown signs of considerable embarrassment about the sending of four U.S. Airborne Warning and Control System (AWACS) planes to this country and reports that Mubarak had asked for them on the basis of Egyptian intelligence reports that Libyan leader Muammar Qaddafi was plotting another coup attempt against the Nimeri government.

A Foreign Ministry spokesman said today that Egypt did not see "any real threat" in the making against Nimeri. "Our information is that it is not that serious," he said.

The spokesman said the Sudanese leader had not asked for any help from Egypt and that no joint maneuvers were taking place or planned between the two armies "for the time being."

Egypt and Sudan are linked by a joint defense pact as well as an "integration charter," and the Egyptian Army has come to the aid of the Nimeri government on numerous occasions in the past. President Hosni Mubarak and Defense Minister Ghazala are scheduled to visit Khartoum Tuesday for a ceremony marking the first meeting of the Higher Council for Integration, a body set up last year to promote closer cooperation between the two countries.

The presence here of West and Lt. Gen. Robert C. Kingston, head of the Central Command, a military command designed to focus on the Persian Gulf and send quick-reaction forces there in an emergency, has also served to heighten speculation about joint U.S.-Egyptian military planning in the present alert over Libya and Sudan.

A U.S. Embassy spokesman insisted that their visit was part of regular consultations between the two governments over the U.S. military aid program and use of Egyptian facilities by U.S. forces and had nothing to do with the tension between Libya and Sudan.

The AWACS incident has come at a time when Egypt is making a determined effort to reassert its role within the Nonaligned Movement, which is about to hold a summit meeting in New Delhi, and to maneuver its way back into the Arab fold from which it was expelled following the signing of its peace treaty with Israel in 1979.

The publicity surrounding Egypt's close military and intelligence links with the U.S. government, as made clear by the Pentagon account of why the AWACS were sent, could easily tarnish the new image that Egypt is trying to project of itself in the Arab and nonaligned worlds.

Evidence that Egyptian officials are aware of this came yesterday in a statement from one insisting that Egypt was "not a party to the strategies of any foreign power and has nothing to do with what the United States or other parties is doing.

"This is in compliance with Egypt's stand in rejecting the policies of East-West polarization, military bases and alliances," the official Egyptian source said.

Egypt is hoping to make a grand reentry into the Nonaligned Movement when Mubarak attends the New Delhi summit next month. At the same time, it is hoping to renew diplomatic relations with a number of Arab states within the next few months.

The first public comment by Mubarak on the current flap over Libya and Sudan came today in an interview in the Kuwaiti daily Al Watan. The Egyptian leader defended what he called Egypt's "unique relationship" with the United States by comparing it to that between India and the Soviet Union and saying that did not mean either country was "aligned" with its superpower ally.

He also defended Egypt's offer of facilities to the U.S. Rapid Deployment Force.

In addition, the Egyptian leader disclosed for the first time that he was mediating between the United States and Iraq in an attempt to restore their diplomatic relations, which Iraq severed at the time of the 1967 Arab-Israeli war.

Mubarak said he had discussed the issue with President Reagan during his visit to Washington in late January but did not indicate what the outcome of this effort had been.

"Only Iraqi President Saddam Hussein may speak about this," he said.

Meanwhile, other reports reaching Cairo from Khartoum during the past 24 hours said Nimeri had nullified the results of recent elections within the country's ruling Sudanese Socialist Union in the capital and dismissed four more members from its ranks.

One of them was Abul Kassim Mohammed Ibrahim, a former secretary general of the union and first vice president who had been elected head of the union's Khartoum branch.

There was no indication whether this had anything to do with the reported Libyan-backed coup plans. But observers here noted that the union is about to hold a congress at which a new leadership is to be elected, including the president of the party and republic.

Thus, the shake-up could be a move by Nimeri before the congress to purge his opponents and ensure his reelection to both posts rather than an action taken in relation to the alleged coup plot.