A confidant of Chancellor Helmut Schmidt, discussing the damaged state of U.S.-West German relations, mentioned a suspicion grown stronger here in recent weeks that some people in Washington would like to hasten Schmidt's downfall and usher in a conservative government.

The confidant described Schmidt as "irritated" by what he termed "the intent of some U.S. politicians to contribute to a change in Bonn."

Such flashes of seeming paranoia between the United States and West Germany, two countries long considered steadfast allies, are not limited to Bonn these days.

A U.S. official, complaining about the support West Germany's ruling Social Democratic Party has shown leftist groups in Central America, saw the handiwork of Willy Brandt, the party's chairman, in a statement last month by world socialist leaders belittling the Salvadoran elections and backing the Sandinista government in Nicaragua.

The Reagan administration sharply criticized the statement, issued by the presidium of the Socialist International, which Brandt chairs, and made a point of releasing a copy of the rebuke through the U.S. Embassy here.

While describing working contacts between them as fine, both U.S. and West German aides acknowledged privately that a deepened sense of suspicion has crept into relations, including a greater readiness by each side to suspect the other of conspiracies.

This mutual wariness, in a relationship still regarded as a bedrock of the Atlantic Alliance, comes after months of accumulated tensions over defense spending, nuclear disarmament, East-West trade and interest rates.

Difficult times in U.S.-West German ties are nothing new. Personal relations between Schmidt and former president Jimmy Carter were notoriously poor. But a number of those interested in transatlantic ties have cited increasingly worrisome feelings of estrangement between the two countries recently.

Speaking in West Berlin last month, U.S. Ambassador Arthur Burns noted a "growing deficiency in understanding between our two countries, a drifting away of the young people in both countries from what had previously been a shared understanding of our common heritage, of our common values, of our common culture--in short an unraveling of the bonds that bind us together."

The basic problem continues to be one of policy differences over how to deal with the Soviet Union. The clash between Bonn's pro-detente stance and Washington's more hawkish approach, which emerged sharply after the Soviet invasion of Afghanistan in December 1979, has reinforced doubts here about the U.S. ability to manage East-West relations without jeopardizing Europe's stability. It also has fed a revival of West German tendencies toward neutralism, which from the 1950s until recently appeared dormant.

In turn, America's irritations with Bonn finally drew outbursts of anti-West German sentiment this year that alarmed officials here.

A confidential report prepared by the Foreign Ministry's planning staff said anti-West German feelings are appearing in the United States for the first time since the founding of the Federal Republic of Germany and give a picture of the West Germans as more interested in trading with the Soviets than in defending freedom.

Concern about West Germany's low image has prompted Bonn to offer to host a June meeting of the 15 North Atlantic Treaty Organization states, with the hope of using the occasion to demonstrate Bonn's loyalty. But a number of groups, including the youth wing of Schmidt's party, have announced plans to march against NATO policies on the day of the meeting.

In a piece of political one-upmanship, the opposition Christian Democrats intend to hold a pro-NATO demonstration on the weekend before the summit--all part of the conservatives' general strategy to pin the blame for poor U.S.-West German relations on Schmidt. The chancellor has been weakened seriously as a result of months of wrangling with the left wing of his party over security and economic policies, and there is insistent talk that the current left-center coalition could crumble before the year is out.

Christian Democrats have been traveling to Washington recently to foster the impression that things would be different if the conservatives were in power here. The most recent of these visitors--Walther Leisler Kiep, the Christian Democratic candidate in the Hamburg elections in June--spoke on his return last week of great concern in the United States about where West Germany is going and whether Schmidt will be paralyzed by his own party's disunity.

This sort of politicking has put U.S. officials in a box. On the one hand, they do not want to turn away approaches from visiting opposition politicians who soon may be running things in Bonn. Nor do they seem inclined to shrink from publicly pressuring Schmidt to join in tightening financial credits for Moscow and to pay for modernization of U.S. troop facilities in West Germany. On the other hand, embassy officials here are sensitive to the role U.S.-West German relations play in domestic politics.

Whether a Christian Democratic government in Bonn would mean smoother relations is disputed by many who argue that West Germany's commitment to cooperative ties with the Soviet Bloc is broadly rooted and would be honored by the conservatives. In addition, Social Democrats claim that a conservative government could result in even greater domestic agitation and polarization.

Admitting that U.S.-West German relations are in need of repair, both governments have designated senior officials to coordinate programs for improving ties.

But one U.S. official remarked that the West Germans continue to compound the problem by poor public relations. A mission last month to European capitals by Undersecretary of State James Buckley to discuss economic sanctions against the Soviets reportedly rated the West Germans the most defensive and pugnacious of the lot.