Stockholders of Communications Satellite Corp. obviously were pleased with the Washington firm's recent offer to buy back up to 2 million shares of common stock at $37 apiece.

So pleased, Comsat reported yesterday, that the Company was swamped by stockholders' tenders to sell 5.635 million shares in an offering that expired Tuesday night.

With about 10 million shares outstanding, the Comsat figures indicated that well over half those shares were offered for purchase. Trading in Comsat stock was halted throughout yesterday's trading session by the New York Stock Exchange.

Since Comsat intends to buy only the 2 million shares, some 3.6 million shares tendered will remain in the hands of current stockholders. Instead of receiving $37 a share, they will own stick expected to be trading at a lower price.

Under terms of the offer, Comsat will buy all shares offered by owners of 10 or fewer shares as of Nov. 11, who tendered all such shares. After Those shares are picked up, Comsat will buy the balance on a pro rata basis.

A spokeswoman for Comsat said yesterday it would take several days to determine the ratio of shares to be bought for share offered by stockholders with more than 10 shares.

Payment for all shares purchased and the return of certificates for unpurchased shares will be made as soon as possible after Dec. 16, Comsat said.

The New York Stock Exchange said that when trading in Comsat resumes, the stock will be listed in its regular way and on a "when distributed basis or WD, applied to the balance of shares tendered that will not be purchased.

Stock exchange traders said quotes for Comsat stock at mid-day yesterday were in a range of $29 to $32. The issue closed Tuesday at $31.75, down down $1 for the day. Comsat WD was quoted at $27 to $30.

Comsat hit a 1977 low of $28.375 earlier this fall after a 1975 Federal Communications Commission decision ordering a rollback in international communications rates was upheld in some major respects by a federal court. After the stock purchase plan was announced, the price immediately moved higher.

In response to the court decision, which Comsat is appealing, the company has moved to restructure its currently debt-free financial base by reducing equity investment and making plans to add debt. FCC decisions have encouraged a mixture of equity and debt investments for utilities, to reduce operating costs and thereby cut rates for consumers.