Taiwanese officials say they have received signals from Washington that the Reagan administration will upgrade relations between the two countries despite repeated warnings by Peking not to do so.

The officials said they have received indications of changes in two relatively minor but highly symbolic areas -- contacts between representatives of the two countries and an increase in the number of Taiwan's unofficial consulates in the United States.

The government here is nervously awaiting the Reagan administration's first hint that it will take the most important step and agree to sell this country sophisticated new weapons.

Any of these moves from Washington to implement the Taiwan Relations Act is likely to arouse new hostility in Peking. The communist government warned last week that relations with the United States would deteriorate if it pursued ties with Taiwan under that act.

Taiwanese officials would not speak in detail about promised changes, but said there have been indications that Reagan will authorize an increase in the number of so-called liaison offices in the United States and said there already appear to be easier contacts between the two countries in Washington.

"In light of President Reagan's philosophy of anticommunism ant the important relationship we must maintain, we have every reason to believe that relations with the United States will improve under his administration," said Premier Sun Yun-suan, the country's second-ranking leader.

He said he is "optimistic" that Washington will permit an increase in the number of liaison offices and that "more frequent contacts" in Washington are "expected."

Two other officials said Taiwan had been encouraged by recent positive signals from Washington. One of them, James Soong, director general of the government information office, said, "We have got indications of improvements in both contacts and [liaison] offices. Nothing has been announced yet, so we are being careful." Soong said his government has been told a former Taiwanese consulate in Boston may be reopened as a liaison office.

Another official, who asked not to be identified, said that "communications are better," between Taiwan's representatives in Washington than during the Carter administration.

Normalization of relations with China required the United States to drop official recognition of Taiwan, which is permitted neither an embassy nor consulates in the United States. The Taiwan Relations Act authorized 14 liaison offices, which act as consulates, but the Carter administration only nine were permitted to open.

There are supposed to be no official contacts between the two countries. Taiwan, under the Carter administration, found it difficult for even non-official representatives in Washington to approach U.S. officials.

But officials here say the rules for such meetings have been changed and that contacts are easier, although they would give no details.

On the most important substantive change, U.S. arms sales, Taiwanese officials say they have received no hints from Washington.

Taiwan's most urgent request is for a new high-performance fighter plane, the FX, but its shopping list also includes Harpoon ship-to-ship missiles and antisubmarine weapons. The Taiwan Relations Act authorizes sales of "defensive" weapons to Taiwan, but the Carter administration shelved such proposed sales out of fear of alienating Peking.

Premier Sun said in an interview that the aircraft is of "paramount concern" because Taiwan's main fighter plane, the F5E, is aging and would be unable to cope with a new generation of fighters planned in Peking. He denied some experts' contention that Taiwan and Peking now have balanced forces and said the mainland now has superiority in "both quality and quantity" of fighters.

Except for the private indications on contacts and liaison offices cited by officials, the government here has had little reason to be pleased with the Reagan administration's performance. As a candidate, Reagan promised closer relations with Taiwan and denounced the Carter administration for failing to implement fully the Taiwan Relations Act.

"There are positive changes and the atmosphere is different," one Foreign Ministry official said this week. "But President Reagan's policy on Taiwan is still under review."

Sources outside the government here said Taiwan's leadership believes it has close friends in the White House but that Asian policy so far has been dominated by Secretary of State Alexander M. Haig Jr.

Taiwan was displeased with Haig's recent promise to consider selling arms to peking, but officials say it came as no surprise.