An emergency international relief effort for earthquake victims was reported on standby last night because the Mexican government had not formally requested assistance.

While friendly governments and private agencies around the world pledged money and supplies to the quake-ravaged area, Mexico said it needs time to assess the damage.

Mexican Ambassador Jorge Espinosa de los Reyes met here with Secretary of State George P. Shultz but confined his request to technical assistance, officials said. The United States is to provide demolition teams and experts to search for persons or bodies thought buried under collapsed structures, they said.

Asked whether Mexico would seek further assistance, Espinosa told reporters: "Let's assess the need. Let's assess the extent of the damage."

Based on the assessment, he said, Mexico may ask for aid from friendly countries, institutions or private donors.

In a reference to the modest nature of the Mexican request, which followed President Reagan's condolences and an offer of U.S. aid, Shultz said: "Mexico likes to confront its problems itself, and we admire that."

Sens. Pete Wilson (R-Calif.) and Lloyd Bentsen (D-Tex.) introduced disaster-relief legislation yesterday. Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) said the panel would take appropriate emergency action at a meeting Tuesday.

Although the Mexican government has stressed its ability to cope with the disaster, private agencies in the United States and Europe are continuing to collect money, medical supplies and food for shipment as soon as a formal request is made.

The League of Red Cross and Red Crescent Societies in Geneva said it has sent an emergency team to assess damage before deciding whether to launch a relief appeal to national Red Cross societies.

A seven-member American Red Cross team flew from here to Mexico City, bearing a portable satellite communications dish and a $250,000 check.

In addition, 30 Swiss rescue workers, accompanied by 16 tons of blankets, tents, rescue equipment and medical supplies, were to leave Zurich late last night. The group included doctors, nine teams of dogs trained in detection and rescue work, and a ton of blood plasma.

In Paris, the Doctors Without Frontiers organization said an eight-member medical team with a one-week supply of medicine and materiel left yesterday for Mexico.

French Foreign Minister Roland Dumas said France had chartered a DC8 airplane to take a team of doctors, while Belgium said it plans to send drugs and supplies Sunday.

Other aid pledges included $380,000 from the European Community's executive commission, $236,000 from the Swedish Red Cross, $88,250 from the Norwegian Red Cross, $81,000 from the British government, $31,000 from the Dutch Red Cross, $500,000 from the Finnish Red Cross, $225,000 from Austrian agencies, $50,000 from the Danish Church Aid Organization and $100,000 from CARE, the international emergency relief organization.

Relief workers said the rescue effort has been hampered by lack of communication with and within the affected area.

The quake destroyed part of the central telephone system in Mexico City, and communication has been largely confined to amateur radio operators, many in the United States, who have been contacting survivors. Officials said the ham operators have been invaluable in helping agencies such as the Salvation Army track Americans' missing relatives and give a picture of what is happening in Mexico City.

A State Department task force has been working around the clock to relay messages from Americans in Mexico City to relatives in the United States. By mid-afternoon yesterday, the department said it had tracked 857 Americans.

The department established a special task force number, (202) 653-7959, and a spokesman said thousands of calls were being received hourly.

If aid is requested, Defense Department spokesman Maj. Fred Lash said military transport planes can provide tents, water containers, plastic bags, dehydrated food and medical supplies.