WASHINGTON (AP) _ France adopted its new system of requiring visas from foreign visitors, including Americans, on advice from the United States, Tourism Minister Jean- Jacques Descamps said Monday.

''We are doing what you have recommended to do in the field of security,'' he told reporters. ''You have no terrorism on your land. As for us, we hope to be soon in the same situation.''

When it was pointed out that Defense Secretary Caspar Weinberger had questioned the value of requiring visas from American tourists, Descamps replied: ''I think simply that if Americans continuue to require a visa, it's because that has a certain usefulness.''

Descamps noted that foreigners coming to the United States are required to obtain visas from U.S. representatives in other countries before they leave for America.

France, which has been struck recently by a wave of terrorist bombings in Paris, has not had such a requirement for American visitors, the minister said.

Descamps also said he believes Americans will understand and accept the new French visa requirement because of existing American standard, although he said he feels not all Americans may be aware that foreigners need visas for visits to the United States.

Until Oct. 1, French visas are being issued to foreigners as they arrive in that country. Those arriving after that date will need to obtain them beforehand from French consulates unless they are citizens of the 11 other countries of the European Communities, or of Switzerland.

Visitors from the former French colonies of Tunisia, Morocco and Algeria need a document called a diptyque, which he said is like a visa.

Descamps said the measure will be renewed in six months unless terrorism has disappeared.

He said he had come to the United States to deal with the practical problems of getting the new system working. He added that French Ambassador Emmanuel de Margerie is in touch with Paris in an attempt to get extra personnel for the purpose. Visas will be issued by French consulates in New York, Washington and nine other U.S. cities, including San Juan, Puerto Rico.

After 2.8 million Americans visited France in 1985, spending an estimated $2 billion, the number of visitors is expected to drop by 30 percent for this year.

Descamps pointed to a survey made between July 25 and Aug. 10, which found only 10 percent of the 1,435 Americans queried said they had changed travel plans in the past year because of terrorism.

As a result, the minister said, he expects any reduction in the number of tourists because of recent bombings in Paris will be only temporary.

Descamps emphasized the importance of other complaints from potential tourists. According to the survey, 36 percent thought of France as a ''very expensive place to visit'' and 4l percent agreed that ''not knowing the language will make enjoying a vacation (there) difficult.''

To French reporters attending a news conference, he outlined a series of measures designed to overcome those objections, including the recruitment of young French students of English to help tourists on the street, and getting hotel proprietors to promise not to raise prices next year after price controls are lifted.