Treasury Secretary Michael Blumenthal arrived here today in a hastily arranged visit and told his hosts that he came at President Carter's request "to reaffirm to the Romanian people and to President Nicolae Ceausescu the importance we attach to Romania's independence and to U.S.-Romanian friendship."

Blumenthal's visit comes just weeks after the Romanian Communist Party chief made a series of speeches clearly rejecting Soviet pressures to increase defense spending and further integrate Romania's army within the Soviet-led Warsaw Pact.

Ceausescu's public defiance has stirred open concern in the Kremlin and quieter yet important repercussions elsewhere in Eastern Europe, according to sources in some of those countries.

The Romanian leader's stand also found high-level support in the White House, which moved quickly to show its feeling. The White House decision to send the treasury secretary has added a touch of additional drama to the situation because Blumenthal, just 48 hours ago, was in Moscow attempting to smooth out problems in the U.S.-Soviet trade climate.

U.S. officials traveling with Blumenthal acknowledged that they were surprised by the White House request to go to Romania. An agenda of trade and economic issues was hastily being put together en route here to provide some semblance of normality to the meeting.

It was clear from the comments of officials and Blumenthal's arrival statement, however, that the most icportant thrust of this visit is to show support for Ceausescu.

What is hard to reconcile, sources acknowledged, was the contrast between the visit in Moscow earlier this week, designed to try to take advantage of a somewhat improved climate between Washington and Moscow, and the quick decision to visit a maverick Communist leader who has clearly and openly just challenged Soviet leader Leonid Brezhnev.

"About all I can say," one official explained privately, "is that we have relations with a lot of countries."

In his initial statement here tonight, Blumenthal said he expected to have "a general political exchange as well as talks on economic and financial issues."

Blumenthal added, however, that "My visit is also a reflection of the value we place on the constructive role that Romania plays in international affairs. We share with Romania a common adherence to the principles of national sovereignty, independence, equality, noninterference and mutual respect. We wish to see these principles, which are firmly rooted in the Helsinki final act, strengthened. These principles are fundamental to stable and peaceful relations among all states."

This evening Blumenthal spent more than two hours with the Romanian foreign minister, Stefan Andrei, and both spoke warmly of ties between the two countries. Blumenthal said he had a personal message from Carter to deliver to Romanian President Ceausescu Saturday.

The secretary's mission here, although obvious, is also delicate since neither the United States nor Romania wants this visit to exacerbate relations further with Moscow. The general thinking among Western officials is that Ceausescu reasoned he could get away with his tough public stand at this time, yet remain within the Warsaw Pact. because of Moscow's problems with China and Eastern Europe generally.

Aside from his outspokenness on the defense issues, Ceausescu has also annoyed the Kremlin with its friendly policy toward China, its unwillingness to break relations with Israel, and its role in the Middle East negotiations.

Ceausescu's rejection of higher defense spending is known to reflect views in other Soviet bloc countries. Last year, Hungarian sources privately complained of the same pressures, which many think are being generated by the Kremlin to help bolster the Soviet defense industry and economy.

Earlier in the days, Blumenthal said he guessed that his trip here had been at the request of the Romanian government; however, it was not clear just how the invitation arose and whether it was the United States or Bucharest that initiated it.

The Romanians had been seeking to attract some high-level U.S. official here, perhaps as a symbolic back-up of Ceausescu's anti-Soviet stand at the recent Warsaw Pact summit meeting.

Sources here said the decision to send Blumenthal was agreed to by Presidential adviser Zbigniew Brzezinski, Secretary of State Cyrus Vance and President Carter. Vance is going to the Middle East this weekend so Blumenthal's availability in Europe was a coincidence.