When word of Soviet President Leonid Brezhnev's death reached Bonn, a senior aide to Chancellor Helmut Kohl asked an American visitor whether President Reagan could be expected to attend the funeral.

Not likely, replied the visitor. This reassured the aide, who for a moment had fretted that the late Soviet leader, as a mischievous parting act, had managed after all to come between West Germany and the United States by upsetting plans for Kohl's meeting with Reagan in Washington on Monday.

With about as much eagerness as a West German chancellor, even a conservative one, dares show for a visit to the Washington of Ronald Reagan, Kohl has been portraying the trip almost as a missionary journey to restore harmony and stability to U.S.-West German relations. In statements during his first six weeks in office, Kohl has promised continuity in the foreign policies conducted by his predecessor, Helmut Schmidt.

But Kohl's stress clearly has been on improving the tone of Western alliance relations while continuing to defend specific West German national interests in Soviet Bloc relations and world trade.

Beyond atmospherics, Kohl has backed this Western emphasis with a pledge of more money for the North Atlantic Treaty Organization--$140 million over four years for its infrastructure fund. He also has given unequivocal support for alliance plans to deploy American Pershing II and cruise nuclear missiles in West Germany at the end of 1983 if no breakthrough comes in U.S.-Soviet arms reduction talks.

Schmidt also was committed to deployment, but dissent from the left wing of his Social Democratic Party raised persistent questions about his government's eventual willingness to follow through.

At the same time, Kohl has underscored Bonn's financial limits at a time of recession here and has reinforced his country's commitment to better Soviet ties.

"On the substance of the matter, Bonn and Washington are likely to meet the same problems," said a high-level West German official. "Anything connected with defense spending, with trade or economics is likely to cause some friction."

The determination of Bonn's new center-right coalition to stand up for national economic interests was dramatically demonstrated last month when the government blocked a U.S.-European compromise on U.S. restriction of steel imports until, in the final minutes, it won a virtual exemption for West German steel and steel-pipe products on the ground that they are not subsidized.

In East-West trade relations, Bonn officials privately have cautioned against expecting quick settlement of outstanding U.S.-European differences on credit terms for Soviet Bloc states or restrictions on high-technology goods, following today's lifting of U.S. sanctions against the Siberia-to-Western Europe gas pipeline.

But officials here hope such points will be kept in the background of Kohl's visit next week. Aides count on the new chancellor's exuberance, his lack of any Schmidt-style tartness, and the warmth with which the Reagan administration is approaching him to get things off to a positive start.

"These people are really a bunch of nice guys," said a U.S. official of a number of Kohl's Christian Democratic aides and ministers. "They differ from Schmidt's people in the way Reagan's relaxed, Southern Californian group contrasted with [former president] Carter's bunch -- they may not be any more willing to compromise, but they are nicer to deal with."

Kohl, who had little experience in foreign affairs before he took over, has impressed diplomatic observers here by the way he stepped into the busy schedule of foreign appointments that Schmidt had left him. Meetings with French President Francois Mitterrand and British Prime Minister Margaret Thatcher have gone well for Kohl.

"I think he's surprised everyone," said a senior Western envoy. "He's gone to the right places, tied down the right feelings without really giving away anything. People are not saying Kohl isn't up to it anymore."

Showing some awkwardness still, Kohl's public comments after meetings with foreign leaders tend to sound like formal communiques. In addition, he refused to take questions from reporters during the summits with the French and British here.