Pan American World Airways yesterday suspended its daily flight to Athens, and many Americans canceled vacations to Greece after President Reagan warned of airport security problems there following the hijacking of Trans World Airlines Flight 847.

Meanwhile, the House swiftly adopted legislation that would pressure foreign governments to assure that their airports meet international security standards, and the Senate voted a $2 million supplemental appropriation for the Transportation Department as seed money for an expansion of the "sky marshal" program the administration is not sure it wants.

TWA, the only U.S. airline other than Pan Am serving Athens, said it is considering the president's request that it "review the wisdom" of continuing to fly there until security problems are solved. It continued twice-daily nonstop flights from New York.

Pan Am's flight to Athens is on a small twin-engine plane from Frankfurt, West Germany, where it connects with flights to the United States. Pan Am said it is booking its Athens passengers on other airlines and will continue to evaluate safety and security to determine when service can be resumed.

Canadian pilots, echoing sentiments expressed earlier by British pilots, asked their government to boycott Beirut airport, where the TWA plane and its three crew members were still being held last night, and to demand tighter security at Athens, where the hijackers and, apparently, their weapons, boarded Flight 847.

With this chorus of condemnation threatening its tourist trade, Greece responded angrily to Reagan's warning and rejected charges from international aviation experts that security is a problem.

Greek Communications and Transport Minister Evangelos Kouloumbis said, "Allegations of improper security for air travelers . . . are absolutely false . . . All the recommended and internationally established secur- ity measures are being applied at Athens air- port . . . ."

Athens' streets were reported filled with American tourists yesterday, but that could change in the weeks to come.

W.R. Brown, head of the AAA Travel Agency, the nation's largest, said, "there is a trend toward heavy cancellations on Greece," despite the fact that many vacationers are booked on package tours with cruises that carry heavy cancellation fees.

"We've had people canceling their travel plans all weekend, and the president's message has precipitated more cancellations this morning. There's no question about it," Joseph H. Stallbaum, an executive with Bartlett Travel Service in Philadelphia, told the Associated Press.

While tourists were making their statement, members of Congress were trying to find a way to make theirs. The House-passed bill, by Rep. Norman Y. Mineta (D-Calif.), was taken up under fast-track procedures and adopted by voice vote after no debate.

"The recent epidemic of hijackings suggests that we have not seen the last of efforts by terrorists to seize aircraft containing U.S. citizens. This is designed to protect our citizens," Mineta said.

The legislation would require the Transportation Department to assess security at foreign airports served by U.S. airlines and notify the public, through posted notices, of airports that fail to meet its standards. Under some circumstances, warnings to passengers would have to be printed on their tickets.

Further, the transportation secretary, with the approval of the secretary of state, could suspend U.S. and foreign flights between the United States and the security-deficient airport, authority that in effect already exists.

After the House acted, bills began to proliferate in the Senate. "We've got so many here we can't even count them now," one Senate source said. The overwhelming thrust of those bills is to require armed marshals on flights.

The Federal Aviation Administration has armed "air marshals," which it uses in special situations as part of its airport- and airplane-security program. FAA security experts, however, are skeptical about the value of armed guards on all flights.

"We don't want to set up the situation where you get a shootout at 40,000 feet," one expert said yesterday. "The best place to stop these things is on the ground."